Abstract: For three phase large welding inverter power supply, three-phase boost topology is introduced as the power factor correction scheme.It' s modulation process is analyzed using vector transformation method.We apply two-loop idea in the whole control system.The inner loop is current loop, and it is used to achieve that the input current is in phase with the input voltage using steady-stage deadbeat control to achieve the best dynamic performance.The outer loop is voltage loop, which control the output voltage to be a constant value and offer instruction for the inner current loop.In order to realize the deadbeat-control that can correct the control error in one switch period, TMS320LF2407A DSP is introduced to the control system, and saber software is used for simulation analyses, and the circuit system and software flow chart is put forward.We realize the digitalation of the control system.The experiment result is analyzed. Power factor by experiment is unit.Three phase input current are in phase with input voltage, and they are relative standard sine wave. The total harmonic distortion of the current is less than 10%, and all of this has meet the international harmonic criterrion.