Abstract: The dissimilarity between the new LCL-type main circuit of soft-switch inverted welding power source and the basic LCL-type is introduced. Mathematical model of new LCL-type of the resonant soft-switch inverted welding power source is established,and analyzed by Matlab soft-ware. In order to test and verify the mathematical model, calculating results of mathematical model is compared with testing results. The arc welding power source has not only high efficiency of series resonant in the whole load range, but also broader soft-switch range. The duty cycle loss of the seconding transformer is eliminated.