As you might suspect, "body percussion" is the sounds that you can make with your body. You might be able to picture this more easily thinking of martial arts than of traditional Chinese dance. It has certainly been incorporated into modern Chinese dance. Think more of the sound of your hand hitting your chest or your foot, or your elbow on your hand, than the sound of your hands clapping.
This Chinese Lion Dance lesson plan for 4th grade, talks about percussion instruments and suggests that students try the rhythms using body percussion before trying the instruments. The unit was designed to cover 3 sessions.