.obj file format limit

.obj 文件保存的内容非常有限：顶点、纹理坐标(最多一套)、法线、三角面；它不支持顶点色、多套纹理坐标(uv2, uv3)、TANGENT、BINORMAL、骨骼权重。

搜索某度，被其内容所误导，花费不少时间 搜索.obj文件支持多套纹理坐标方式，未果！

• 后在Blender中尝试导出带有2套纹理坐标的模型，.obj中只能带一组纹理坐标，而.fbx可以带2套！
• obj文件中，若带有纹理坐标，其面索引模式必须为：f v/vt/vn 明确指定纹理坐标索引才行

The .obj file format only supports a single UV map per object. There is no way to export an .obj file from blender with multiple UV maps. What you should do is use another file format such as FBX which does support multiple UV maps per object.

Reference: https://blender.stackexchange.com/questions/8229/how-to-export-to-obj-with-separate-map-channels