Abstract: The physical model including input and output rectifier filter,inverter and buck circuits was founded.According to actual parameters of every component,the modeling and simulation of the main loop circuit and digital control system were studied through the nonlinear interface model.Finally,the mathematical model of dynamic welding process was established to form the welding power source system model,and variation of physical quantities and dynamic response process were analyzed quantitatively.Simulation results predict the work process of the pulsed MIG welding power source,show the significance of welding current control and arc voltage control,which lay the foundation for further research.