Abstract: Gas metal arc welding parameters were optimized by orthogonal experiments for 2mm thick uncoated DP780 steel plate.The influences of five factors including wire feeding rate,welding speed,arc voltage,wire extension and welding angle on tensile strength of DP780 lap joints were discussed.The range analysis and variance analysis proved that wire feeding rate and welding speed are the main influencing factors on the tensile strength of the join,and the other factors show no regularity to tensile strength.An approximate mathematical model to control the tensile strength of the joint was obtained by fitting the proximate curve through multiple regression analysis,which revealed the regularity of effects of main welding parameters on the tensile strength of the joint.