How I can export models in msh to obj format ?
Here's how I would do it, though there might be other ways:
Drag the .msh into SWBFViewer and then click File>export to .vrml. You can then convert the .vrml to .obj in a program like Blender.
Alternatively you could get a .obj export plugin for XSI but I've never used this and I don't know if it works.
Thanks