Abstract: In the diesel engine electric control system,the stability of common rail pressure,which is one of important factors of deciding oil injection quantity and rate,exerts great influence on the whole system.The pressure overflow control method is an effective way in the high pressure oil injection system to stabilize the common rail pressure.The mathematic model of electromagnetic pressure overflow valve was established by dividing t he models into five subsystems according to its internal features,i.e.the circuit subsystem,the magnetic circuit subsystem,the mechanical subsystem,the hydraulic subsystem and thermal subsystem.The analysis and simulation of the model comprehensively consider the major factors in the working process of electromagnetic valve,which provide a good basis for the optimization design of the common rail electromagnetic pressure overflow valve.