Abstract: The traditional AC power supply of seam welding has the shortages of low heat efficiency, long Zero-Crossing Timing as well as welding heat. In order to overcome these shortcomings, a new type of AC inverter welding power supply was developed. The power supply, whose inverter switch signals are generated by STM32 internal pulse modulation module, takes the 32 bit microcontroller STM32F103RCT6 as the main control core and works with sampling system to realize the goal of accurate control by the way of PI algorithm. The main power circuit, the inverter control mode along with the hardware and software design of the control system about the AC seam welding power supply were studied in details. The results indicate that the AC seam welding power supply is reasonable and reliable, which boasts fast dynamic responding, adjustable frequency, high stability as well as excellent performance of constant-current control, which is suitable for micro precision seam welding.