(need help )why different with unity and ue4 about fbx vertex normal,this is ue4 bug?

how to make ue4 normal the same as unity?

the issue isn’t normals but the shading. The point the light is hitting to be more precise.

these vector are float ,the same as unity shader

Vectors have nothing to do with anything here. Its your directional light within the scene along with the rendering options for your mesh that need adjustment.

the last picture is only show the vertex nomal vector with color,it seems very different with unity import .So i guess it is fbx mesh importing bug.

You might need to invert the green or red color channels for UE4 to use it, or swap them

the last picture had inverted red,and swap green and blue