I want to implement a plug-in function, how to get all SkeletalMesh in the plug-in, and hide its material

How to get all the SkeletalMesh in the Level?

Same way as you would do that in C++ project, either by TActorIterator or UGameplayStatics::GetAllActorsOfClass

Editor is using world instance in level editor same as you would do in normal game play, and you can get UWorld of level editor via GEditor->GetEditorWorldContext().World()

Thank you for your reply. It’s very helpful. I’ve got skeletalmesh and the specified material. How do I hide them?

What do you mean by “hide”? hide actors with them?