Abstract: This pape studies the optimum design theory and practice of hight frequency high-power pulse transformer of arc welding inverter.From the point of minimizing the total transformer loss,the optimum ratio of copper loss to core loss and the optimum copper loss ratio of primary winding to second winding are developed.On the basis of heat transfer theory and experiment,the thermal model of the transformer is derived.A local optimum design method based on the maximum allowing temperature rise is proposed and tested by expeiments.