Aluminum　(Al)　alloy　welded　structures　are　widely　used　in　industry　and　daily　life,　while　welded　joints　are　easily　produced　defects,　including　macro　and　microscopic　defects.　It　is　a　hot　topic　to　study　the　effect　of　microscopic　defects　on　the　properties　of　welded　joints.　In　this　paper,　a　two-dimensional　rate-dependent　crystal　plasticity　model　is　established　by　using　a　numerical　model,　and　then　the　mechanical　behaviors　of　welded　joints　with　micropores　under　tensile　load　is　simulated　in　a　mesoscale.　The　mechanical　properties　are　described　by　varying　the　sizes　and　positions　of　micropores.　The　stress-strain　response,　equivalent　plastic　strain　and　equivalent　stress　distributions　of　polycrystalline　Al　alloy　welded　joints　with　different　micropores　are　obtained.　The　results　verify　that　those　micropores　have　certain　impact　on　the　start　of　slip　systems　and　the　ability　of　resisting　the　deformation　of　polycrystalline　joints.　Compared　with　the　positions　of　micropores,　the　sizes　of　micropores　have　a　greater　impact　on　the　mechanical　properties　of　the　polycrystalline　joints.　©　2019　Published　under　licence　by　IOP　Publishing　Ltd.