Abstract: Based on the study of droplet transfeormation and inverter arc welding power surface tension transformation (STT) in CO₂ arc welding which has very low spatter has been used in pipe root-welding.In this paper,a simulation model is presented for STT in CO₂ arc welding which integrates current inverter welding power and arc model,and is designed to simulate the effect of droplet to arc length in arc phase and the effect of conductor to the current decrease rate in short circuit phase.The result of simulation is almost same as experiment,and shows the conductor in output loop is a key to realize low spatter.