The　stress　and　strain　in　Aluminum　cylinder　longitudinal　and　circumferential　weld　seam　are　simulated　by　finite　element　analysis　tools-ANSYS.　Tube　structure　in　aerospace　is　welded　by　the　variable　polarity　plasma　arc　welding　process.　According　to　the　characteristics　of　variable　polarity　plasma　arc　weld,　surface　heat　source　and　cylindrical　heat　source　are　used　to　simulate　variable　polarity　plasma　arc　weld.　The　program　which　is　used　to　achieve　loading　and　moving　variable　polarity　plasma　arc(VPPA)　welding　heat　is　wrote　by　using　the　ANSYS　parametric　design　language(APDL)　in　ANSYS　software.　The　same　structure　in　different　type　of　weld　is　presented　by　the　different　ways　of　loading　heat　source.　The　use　of　sweep　meshing　method　to　build　complex　cylinder　structure　analysis　model　is　proposed.　Through　the　simulation　results,　the　complex　cylinder　welding　deformation　evolution　process　is　explained.　It　is　found　that　longitudinal　seam　ends　have　obvious　stress-strain　release　in　the　process,　and　cross　section　deformation　directly　influenced　the　size　precision　of　whole　structure.