Because the source that comes with Kali is foreign, it is often impossible to install or update software packages due to network problems. And foreign sources are very slow. So we directly use domestic sources, which is convenient and fast.
Before modifying the apt source, you need to set the root password of Kali
Open Kali's terminal
sudo passwd root
Enter the password of the dq user
Enter the root user password that needs to be set
Enter the root password verification that needs to be set again
passwd: password updated successfully indicates that the password has been successfully modified
Switch to the root user and set the apt source
su - root 
Modify the apt source to the source of the University of Science and Technology of China
vim /etc/apt/sources.list 
Comment out the original official source, and add 2 sources from the University of Science and Technology of China at the end of the file
deb https://mirrors.ustc.edu.cn/kali kali-rolling main non-free contrib
deb-src https://mirrors.ustc.edu.cn/kali kali-rolling main non-free contrib 
After changing sources.listthe file please run apt updateupdate index to take effect.
apt update
Here I show that 591 packages can be updated, this can be ignored, Kali's apt source has been replaced with the domestic source of the University of Science and Technology of China.