Abstract: Due to the complexity of the welding process, it was difficult to obtain the analytic mathematical model of dynamic process of molten pool, that was why the modeling of welding process became a major problem to the welding process control.For the purpose of establishing the model of dynamic process of molten pool of the electron beam welding.The step-response method was used to determine the type and structure of mathematical model of electron beam current and molten width of titanium alloy electron beam welding, the parameters of model were calculated, and the transfer function model of electron beam current and molten width was established.The Z-N empirical formula was used to obtain the parameters of PID controller based on the mathematical model.On this basis the MATLAB/SIMULINK platform was used to establish the model of PID control system of molten width of titaniumalloy electron beam welding.The simulation experiment was done and the results show that the dynamic performance and steady-state performance of designed control system are eminent.