The　CMT　technology　is　adopted　to　directly　fabricate　thin-walled　parts　and　the　process　parameters　are　optimized　to　overcome　the　shortcomings　of　complex　procedure　and　uneven　performance　or　low　accuracy　of　the　fabricated　part　in　the　traditional　manufacturing　process.　Thin-walled　parts　are　taken　as　research　objects　to　establish　a　3D　response　surface　model　with　the　wire　feed　speed　and　the　ratio　of　wire　feed　speed　to　welding　gun　travel　speed　as　input　variables,　and　the　layer　width　and　the　ratio　of　layer　width　to　height　as　output　variables　to　predict　the　geometry　features　of　the　parts.　The　effects　of　the　arc　length　and　the　gun　travel　angle　on　deposition　procedure　and　finally　formed　shape　are　studied.　The　behaviour　and　characteristics　of　the　transfer　are　analyzed　by　using　a　high　speed　camera,　and　the　action　mechanisms　of　the　process　parameters　on　formed　shape　are　described.　Experimental　results　show　that　the　accuracy　of　the　geometric　feature　prediction　model　is　higher　and　its　prediction　error　is　less　than　5%.　The　humping　defects　on　the　side　of　thin　wall　are　avoided　by　using　a　-15%　arc　length　modification.　The　surface　quality　of　the　thin-wall　parts　is　clearly　improved　when　the　travel　angle　reaches　10°.　It　is　not　applicable　to　use　push　angle　for　deposition　due　to　high　probability　of　humping　defects.　©　2019,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.