传统的ComboBox没办法添加自定义图标，存在模糊的缺点。采用了自定义的图标，可以解决该问题。
ComboBoxStyle
<Style TargetType="ComboBox" x:Key="ComboBoxStyle34x30">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBox">
<Grid Background="#F7FDF7">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="30" />
</Grid.ColumnDefinitions>
<TextBox Grid.Column="0" IsReadOnly="{TemplateBinding IsReadOnly}" Text="{TemplateBinding Text}" VerticalContentAlignment="Center"></TextBox>
<Border Grid.Column="0" BorderThickness="1,1,0,1" BorderBrush="#FFABADB3" CornerRadius="1,0,0,1"></Border>
<Border Grid.Column="1" BorderThickness="0,1,1,1" BorderBrush="#FFABADB3" CornerRadius="0,1,1,0">
<ToggleButton Style="{StaticResource ComboxStyleBtn34x30}" IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Release"></ToggleButton>
</Border>
<Popup IsOpen="{TemplateBinding IsDropDownOpen}" Placement="Bottom" x:Name="Popup" Focusable="False" AllowsTransparency="True" PopupAnimation="Slide">
<Border CornerRadius="1" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{TemplateBinding ActualWidth}" x:Name="DropDown" SnapsToDevicePixels="True">
<Border.Effect>
<DropShadowEffect Color="Black" BlurRadius="2" ShadowDepth="0" Opacity="0.5"/>
</Border.Effect>
<ScrollViewer Margin="4,6,4,6" Style="{DynamicResource ScrollViewerStyle}" MaxHeight="{TemplateBinding MaxDropDownHeight}" SnapsToDevicePixels="True" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" CanContentScroll="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" Background="White"/>
</ScrollViewer>
</Border>
</Popup>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>ComboxStyleBtn34x30
<Style TargetType="ToggleButton" x:Key="ComboxStyleBtn34x30">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border x:Name="ComboBoxButton">
<Border.Background>
<VisualBrush>
<VisualBrush.Visual>
<Canvas Width="34" Height="30">
<Path Data="M0.5,5.5 C0.5,2.7385763 2.7385763,0.5 5.5,0.5 L116.5,0.5 C119.26142,0.5 121.5,2.7385763 121.5,5.5 L121.5,46.5 C121.5,49.261424 119.26142,51.5 116.5,51.5 L5.5,51.5 C2.7385763,51.5 0.5,49.261424 0.5,46.5 z" HorizontalAlignment="Left" Height="30" Stretch="Fill" Stroke="#FFCDCDCD" VerticalAlignment="Bottom" Width="34" >
<Path.Fill>
<LinearGradientBrush EndPoint="0.5,1" Opacity="0.99" StartPoint="0.5,0">
<GradientStop Color="#FFDCE0E3" Offset="0.456"/>
<GradientStop Color="#FFD8DDE0" Offset="0.828"/>
<GradientStop Color="White" Offset="0.033"/>
<GradientStop Color="White" Offset="0.979"/>
</LinearGradientBrush>
</Path.Fill>
</Path>
<Path Stroke="#FF4E7BBF" Height="1.887" Canvas.Left="8.997" Canvas.Top="15.353" Width="10.77" StrokeThickness="2.5" RenderTransformOrigin="0.5,0.5" Data="M1.25,1.25 L9.52,1.25 z" Stretch="Fill" Fill="#FF4E7BBF">
<Path.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform Angle="42.475"/>
<TranslateTransform/>
</TransformGroup>
</Path.RenderTransform>
</Path>
<Path Stroke="#FF4E7BBF" Height="1.887" Canvas.Left="16.119" Canvas.Top="15.277" Width="11.034" StrokeThickness="2.5" RenderTransformOrigin="0.5,0.5" Data="M1.25,1.25 L9.784,1.25 z" Stretch="Fill" Fill="#FF4E7BBF">
<Path.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform Angle="-41.32"/>
<TranslateTransform/>
</TransformGroup>
</Path.RenderTransform>
</Path>
</Canvas>
</VisualBrush.Visual>
</VisualBrush>
</Border.Background>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="AreAnyTouchesOver" Value="True">
<Setter Property="Background" TargetName="ComboBoxButton">
<Setter.Value>
<VisualBrush>
<VisualBrush.Visual>
<Canvas Width="34" Height="30">
<Path Data="M0.5,0.6165023 C2.997254,0.59726893 2.8098952,0.65987028 2.842921,0.60897645 L107.3705,0.37740332 C116.99575,0.91922384 121.5,4.2233519 121.5,6.9847756 L121.5,44.756377 C121.90224,49.208879 109.43357,51.497385 105.87162,51.5 L5.5,51.5 C2.7385763,51.5 5.4499507,51.480567 0.5,51.506233 z" HorizontalAlignment="Left" Height="40.094" Stretch="Fill" Stroke="#FF4E7BBF" VerticalAlignment="Bottom" Width="38.003" />
<Path Data="M0.5,0.6165023 C2.997254,0.59726893 2.8098952,0.65987028 2.842921,0.60897645 L107.3705,0.37740332 C116.99575,0.91922384 121.5,4.2233519 121.5,6.9847756 L121.5,44.756377 C121.90224,49.208879 109.43357,51.497385 105.87162,51.5 L5.5,51.5 C2.7385763,51.5 5.4499507,51.480567 0.5,51.506233 z" HorizontalAlignment="Left" Height="35.927" Stretch="Fill" VerticalAlignment="Bottom" Width="33.49" Canvas.Left="2.375" Canvas.Top="2.042" StrokeThickness="0" >
<Path.Fill>
<LinearGradientBrush EndPoint="0.5,1" Opacity="0.99" StartPoint="0.5,0">
<GradientStop Color="#FF8EC3F2" Offset="0.456"/>
<GradientStop Color="#FF86AFDF" Offset="0.828"/>
<GradientStop Color="#FF91CBF9" Offset="0.033"/>
<GradientStop Color="#FFD9E0E6" Offset="0.979"/>
</LinearGradientBrush>
</Path.Fill>
</Path>
<Path Stroke="White" Height="1.887" Canvas.Left="12.08" Canvas.Top="21.603" Width="10.77" StrokeThickness="2.5" RenderTransformOrigin="0.5,0.5" Data="M1.25,1.25 L9.52,1.25 z" Stretch="Fill" Fill="White">
<Path.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform Angle="42.475"/>
<TranslateTransform/>
</TransformGroup>
</Path.RenderTransform>
</Path>
<Path Stroke="White" Height="1.887" Canvas.Left="19.202" Canvas.Top="21.527" Width="11.034" StrokeThickness="2.5" RenderTransformOrigin="0.5,0.5" Data="M1.25,1.25 L9.784,1.25 z" Stretch="Fill" Fill="White">
<Path.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform Angle="-41.32"/>
<TranslateTransform/>
</TransformGroup>
</Path.RenderTransform>
</Path>
</Canvas>
</VisualBrush.Visual>
</VisualBrush>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Background" TargetName="ComboBoxButton">
<Setter.Value>
<VisualBrush>
<VisualBrush.Visual>
<Canvas Width="34" Height="30">
<Path Data="M0.5,5.5 C0.5,2.7385763 2.7385763,0.5 5.5,0.5 L116.5,0.5 C119.26142,0.5 121.5,2.7385763 121.5,5.5 L121.5,46.5 C121.5,49.261424 119.26142,51.5 116.5,51.5 L5.5,51.5 C2.7385763,51.5 0.5,49.261424 0.5,46.5 z" HorizontalAlignment="Left" Height="30" Stretch="Fill" Stroke="#FF4E7BBF" VerticalAlignment="Bottom" Width="34" >
<Path.Fill>
<LinearGradientBrush EndPoint="0.5,1 " StartPoint="0.5,0">
<GradientStop Color="White" Offset="0.983"/>
<GradientStop Color="White"/>
</LinearGradientBrush>
</Path.Fill>
</Path>
<Path Data="M0.5,5.5 C0.5,2.7385763 2.7385763,0.5 5.5,0.5 L116.5,0.5 C119.26142,0.5 121.5,2.7385763 121.5,5.5 L121.5,46.5 C121.5,49.261424 119.26142,51.5 116.5,51.5 L5.5,51.5 C2.7385763,51.5 0.5,49.261424 0.5,46.5 z" HorizontalAlignment="Left" Height="25.67" Stretch="Fill" VerticalAlignment="Bottom" Width="29.333" Canvas.Left="2.331" Canvas.Top="2.163" >
<Path.Fill>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FF86AEDE" Offset="0.812"/>
<GradientStop Color="#FF91CCFA"/>
<GradientStop Color="#FF8DC1F0" Offset="0.565"/>
<GradientStop Color="#FFDFE3E6" Offset="1"/>
</LinearGradientBrush>
</Path.Fill>
</Path>
<Path Stroke="White" Height="1.887" Canvas.Left="9.565" Canvas.Top="15.08" Width="10.77" StrokeThickness="2.5" RenderTransformOrigin="0.5,0.5" Data="M1.25,1.25 L9.52,1.25 z" Stretch="Fill" Fill="White">
<Path.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform Angle="42.475"/>
<TranslateTransform/>
</TransformGroup>
</Path.RenderTransform>
</Path>
<Path Stroke="White" Height="1.887" Canvas.Left="16.687" Canvas.Top="15.004" Width="11.034" StrokeThickness="2.5" RenderTransformOrigin="0.5,0.5" Data="M1.25,1.25 L9.784,1.25 z" Stretch="Fill" Fill="White">
<Path.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform Angle="-41.32"/>
<TranslateTransform/>
</TransformGroup>
</Path.RenderTransform>
</Path>
</Canvas>
</VisualBrush.Visual>
</VisualBrush>
</Setter.Value>
</Setter>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>