How to make custom shader?

How to make a custom shader , or modify default shader in engine? is there any tools or document ?

You can add .usf files with your own hlsl code to engine/shaders. #include the filename in material_template.usf to access its functionality in the material editor from custom nodes.

thank you, is there any tools for easily edit a usf file?

It’s just hlsl. You can use visual studio, or any text editor, like notepad.