Abstract: This paper introduces the design method of a new capacitor stored energy spot welding machine. The new power uses super capacitor to form low voltage capacitor groups instead of high voltage one.The capacitor is charged with direct current chopper circuit, which takes IGBT as the main power machine piece, SKHI22AH4 as the drive circuit, SG3525 as the control chip for PWM, and current feedback in order to get the constant current. In the discharge circuit, the large current is discharged directly through large power SCR without the welding transformer. For the software, 80C552 is the main control chip of the controlling system, so the welding machine could work automatically.The new machine designed has already been used in production and the fine effect was gained to improve the welding quality.