The　U-I　mode　inverter　P-MAG　welding　machine　controlled　by　80C196KC　16-bit　single　chip　computer　was　designed.　By　sampling　the　voltage　and　current　of　arc　in　the　welding　process,　the　arc　voltage　is　kept　constant　in　the　peak　period　and　welding　current　is　kept　constant　in　the　base　period.　Arc　length　self-adjustment　was　realized　by　changing　of　the　peak　current,　and　the　pulse　parameter　was　optimized　to　make　sure　the　one　pulse　one　droplet　transfer　mode.　The　experimental　result　indicated　that　the　welding　machine　has　perfect　welding　performance.