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.　©,　2015,　Harbin　Research　Institute　of　Welding.　All　right　reserved.