Abstract: The authors adopt a digital signal processor (DSP) as a core of control to implement the complicated algorithm so as to meet the need of the power factor correction (PFC) of three phases arc welding inverter. In the meanwhile, when different control methods are chosen, the flexibility of DSP is occurred because of its fast speed characteristic. The principle of space vector modulation is also studied, and introduced to realize the PFC of three phases arc welding inverter based on DSP controlled system. Good harmonic suppression result and unit power factor are achieved. In addition, dynamic load of arc welding inverter is tested to confirm the feasibility of PFC of three phases arc welding inverter mainly controlled by a DSP chip.