Abstract: The developed SCR inverter type stud welding power source uses a series half-bridge inverter in the main circuit and is controlled by the MCS-51 microcomputer. Firstly,the main circuit priciple of this kind of stud special welding power source is introduced and the work procedure is analysed in this paper. Secondly, the basic structure, circuit and work priciple of the control system is introduced, which includes the electric magnet circuit for rasing welding torch, the switch circuit for changing electric current, keyboard and display unit interface circuit. Thirdly, the main programme chart of welding is given. Finally, the spectial stud welding power source is compared with the ordinary stud welding power source by testing. This kind of microcomputer-controlled stud welding power source has the following advantages: high control precision, stable control process,friendly operation surface and very convenient for man-machine conversation. The maximum stud diameter is 12 mm. It will have extensive practical prospects in the manufacture field of domestic cars.