Abstract: The simulation tool inMatalab was used to characterize the resistance welding inverter system and to optimize the circuit parameters.The system output waveforms were analyzed and simulated for different filter capacitors and secondary loads.The result shows that the filter capacitor should be selected so that the rectifier output current is intermittent pulsative, and load current is supplied by the rectifier at voltage crest and by the capacitor at voltage trough.The secondary current rises as exponential fuction and its rising rate is a inverse proportional to the secondary inductance.It will finally reach a maximum value which is not affected by the inductance when provided the welding time is long enough.