the number of mesh vertices increases when the object is imported unity from Max.

For example the cube in the picture.However,the cube should only has 8 vertices.Someone could help me or give me some reason?Tanks a lot!!!

3DS max allows you to ‘weld’ vertices, which is just shorthand for pairing up vertices so all values are equal and a change to one will change the other - welding does not reduce the actual vertex count, which is what Unity uses. In your Max model, the corners are welded; in Unity welds are meaningless, since when you send a mesh to the GPU for rendering you need a different normal for each of the 3 vertices in each corner (corresponding to the 3 faces that end at that point). So your total vert count would be 6 sides * 4 corners / side = 24 verts.

In Unity you *can* reuse vertices in multiple triangles, so you *could* create an 8-vertex cube, but that would mean that the cube would have no hard edges - it would be rendered as if all edges were rounded. This is because you would have to combine the 3 normals and tangents at each corner into 1 shared normal and tangent.