Abstract: The test platform of double-wire MIG welding process was built that composed by Tandem double-wire welding system,signal data acquisition system,high-speed camera(photograph) system and pulse control system.The effects of peak pulse voltage on metal transfer and formation of weld were studied by use of this test platform.The result proves that the effect of the peak pulse voltage of front wire on metal transfer is very obvious.The mode of metal transfer is spray transfer when the peak pulse voltage of front wire is lower.The mode of metal transfer is one pulse and one droplet transfer when the peak pulse voltage of front wire is higher.If the peak pulse voltage of front wire is too high,the mode of metal transfer is becoming drop transfer.The higher peak pulse voltage of front wire was,the bigger weld width and penetration were.The appearances of weld become deterioration when the peak pulse voltage of front wire is excessively high.