Simulation research on triggering current is the kernel of electromagnetic railgun investigation， based on its equivalent electric circuit， the models of pulsed power， rail， armature， sliding electrical contact between armature and rail are established， and the electromagnetic railgun simulation model is established by integrating the component models together. By means of Dommel-EMTP（electromagnetic transient program）algorithm， the triggering current and voltage of every pulse forming unit are simulated， then the total discharging current， velocity and displacement of armature are solved. Compared with the tested date， the relative error of simulation results of total discharging current and armature muzzle velocity is less than 4% ， which indicates the effectiveness and accuracy of the model and provides basic method for further research on electromagnetic railgun.