Abstract: Because arc welding converter is nonlinear, discrete system, the exactitude analytic resolution is difficult to obtain, a average state equation is built in this paper by using state space analysis method.The mathematics model of converter is obtained after linearization.The model is a two-order oscillate element. According to the parameters in arc welding converter that are satisfied the relation ((1)/(RC))² > >(4)/(LC),so the model can be simplified as a integer series with a one-order inertia element.Based on the model, analysis and revising in frequency domain,several parameters are taken around the theoretical revising parameter,both resistance load and welding experiments are carried out. The results of experiments are matched with theoretical analysis. Practicality analysis have been done in the load which is sudden open circuits or short circuits, start and stop the converter. The results shows that frequency method can be used in arc welding converter. The model deputizes for the basic characteristic of the system,it is determined by the structure,parameters and the static conduct ratio of the system.It can be used in design and analysis of the arc welding converter.