why is this?(I m Chinese my English is bad please use photo to tell me THANKS!! )


That is bleeding
You need wall/floor/ceiling to line up exactly in the corners.
If they extend beyond then the surface on the outside can receive shadow or light and that can become visible on the inside.

thanks but what about is material color different? (i use static skylight)

Perhaps you need to play with the Texture Coordinates node for your material - it plugs into all textures you use for your material and you can scale the texture size up or down. Did that door mesh have a texture on it in the program you modelled it in? If it did, is it the same as the texture in Unreal?

提高 lightmap 分辨率应该可以解决上面的大部分问题,具体可以看