Abstract: The axial force in plasma arc is measured under different welding conditions.The effects of the parameters, such as welding current, plasma gas flow rate, electrode setback and nozzle height, on the force in plasma arc are investigated and quantitatively analyzed by significance test method.It reveals the relationship between the weld quality and the matching of parameters in plasma arc welding process.The necessary conditions to obtain stable keyhole plasma arc welding process are also discussed in this paper.This work may be as a useful tool for the understanding of the parameters matching and process optimization in plasma arc welding.