Abstract: Soft-switching arc welding power source of resonant type of new LCL-type was designed on the basis of the principle of main circuit and the main parameter of the circuit was determined.The contents include calculation for parallel connection inductance LP and the primary capacitance of main transformer,no-load voltage ratio and maximum duty ratio of the transformer.Experiment about the arc welding power source was done in the light of designed parameters.The experimental results indicated that the power source can work well with soft-switch.So the design is reasonable and valid.