Gas　metal　arc　welding　parameters　were　optimized　by　orthogonal　experiments　for　2　mm　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.