This paper investigates the piston motion control strategies of a single piston hydraulic free-piston diesel engine, which is intended to be a power supply for hydraulic propulsion systems. The Cycle fuel mass is determined by engine displacement and load. A closed loop control method is used in fuel injection timing control strategy to make the position of bottom dead center steady possibly. In each cycle, the injection timing is corrected by the compare between real bottom dead center position and designed bottom dead center position. The test results indicated that the advanced fuel injection control presented in this paper could improve engine performance and operational stabilization.