There are some images pasted in the named board, but when I export macro library, then import, the images were gone, only name left.
How can I backup them?
You would have to transfer the Keyboard Maestro preferences folder. See:
How do I backup / transfer my installation to another Mac?
https://wiki.keyboardmaestro.com/manual/How_do_I#How_do_I_backuptransfer_my_installation_to_another_Mac