How Can I import 3d graphics into After Effects CS6???

As far as I know, you can't with the current versions! I did a few researches a few months ago and aparently in an older version you could use a 3D model using the Photoshop's 3D features (aparently gone on the newer versions) and then export to AFX.

Although you can use a few other techniques to "merge the 3D" into AFX, like motion tracking and camera's z-depth information (using the .rpf file format - look for it on Google for more details!)

Don't know if it helps, but the actual 3D merge into AFX, as far as I know, isn't possible!

Here is the answer in 4'39"
https://www.youtube.com/watch?v=n6pgRt5kDrI
Injoy
importing animation is more complicated

The user should have Element 3d plugin for After Effects.
For importing in After Effects the 3d model should be in .obj format all textures should be applied after import .