An energy conversion system was developed to convert the human body energy into electrical energy by means of the piezoelectric ceramic to substitute or charge automatically the battery under special conditions.This mechanism,which was fixed at the knees of people,was designed to press piezoelectric ceramics (PZT) in order to collect the energy created by walking people.The energy harvester selectively engaged power generation at the end of the swing phase.A piezoelectric generator was designed.The electrical energy generation performance was investigated experimentally.This method well suited for charging powered prosthetic limbs and other portable medical devices.