Abstract: The paper introduces the real value of the switching power source designed by authors and the systemic analysis of the principle and constitution of the power supply including the microcomputer controlling system. The authors put forward some viewpoints about the new welding power source. The power source which is controlled by the microcomputer system in this paper adopts the giant transistor (GTR),and have it work in both the condition of "on" and "off".Therefore,it overwhelms lower efficiency of analogue transistor power source,and keeps a stable operation state. In the meantime,the power source makes use of single chip microcomputer controlling technology and realizes the function of previous setting up the welding parameters. This power can also modify the welding voltage U_f through feedback controlling so that gets constant voltage characteristic.