Abstract: Gas metal arc welding (GMAW) has been widely used in automatic welding,where the quality problem often appears during the disturbance.So the on-line quality automatic monitoring has been required in manufacturing.In order to realize the goal of zero defection and meet the demands of the on-line quality monitoring well,the paper uses the electrical signal of welding process,and puts forward to the method of multivariate statistical process control on the basis of analyzing the limitation of statistical process control.At the mean time,the on-line monitoring platform has been developed,where experiments have verified the feasibility.