Abstract: Gas metal arc welding parameters were optimized by orthogonal experiments for 2 mm thick uncoated DP780 steel plate and 2 mm uncoated MS1180 steel plate. The influences of wire feeding rate, welding speed, arc voltage and welding angle on tensile strength of special lap joints were discussed. Statistical analysis of orthogonal experiments and results proved that wire feeding rate and welding speed are the main influencing factors on the tensile strength of the joints, and the welding angle has less influence on tensile strength. The optimal process parameters and an approximate mathematical model to control the tensile strength of the joint were 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.