Free piston stirling engine linear motor power generation system earns widespread attracts for the possession of properties as highefficiency, long term on track and broad application resource. Position detection plays an important part on the Free Piston Stirling Engine Linear Motor Power Generation System, from which the rationality and stability of the motor design working system can be analyzed. To acquire the dynamic procedure from the starting powerdriven status to the power generating status of Free Piston Stirling Engine Linear Motor Power Generation System, and to decrease the system volume and improve the leakproofness, a pressure wave testing method based on sensorless position detection was designed. This method makes use of a new pressure wave sensor, accompanied with appropriate powersupply, conditioning and acquisition circuit, it detects the position of the engine’s active cell in real time, thus to realize the control of the power generating system.