I am new at game development want to know that how can I implement bullet physics in libgdx. I searched lot of things on Internet but nothing found worthy.
As I mentioned in my comment above, this question is a bit overbroad, but here's the source code for the JNI bullet engine in libgdx. And here's the wiki. The Bullet User Manual is a pdf file located in the root of the Bullet Physics SDK, which might make a good place to start.
You'll need to add gdx-bullet.jar and gdx-bullet-natives.jar to your desktop project, and gdx-bullet.jar to your Android project. You’ll also need to copy the libgdx-bullet.so files from the extensions/gdx-bullet/armeabi and armeabi-v7a folders to your Android project’s libs/armeabi and armeabi-v7a folders of course.
And there's this from the google codebase:
There's a good deal more information at the links provided above.