In　order　to　adapt　to　the　development　trend　of　a　lightweight　automobile　and　meet　the　safety　requirements　of　key　automotive　parts,　it　is　necessary　to　study　the　relationship　between　microstructure　and　mechanical　properties　of　the　dissimilar　and　different　thickness　materials　welded　joint.　In　this　work,　a　dissimilar　welded　joint　of　high　strength　vehicle　steel　ASSAPH440　with　2.0　mm　thickness/galvanized　cold　rolled　sheet　DC52D+ZF45　with　2.6　mm　thickness　formed　by　CO2　laser　welding　was　studied.　The　microstructure　of　the　welded　joint　was　analyzed　by　metallographic　structure　and　mechanical　properties　were　discussed　in　terms　of　their　tensile　strength　and　microhardness.　The　results　indicated　that　a　high-quality　welded　joint　with　an　average　tensile　strength　of　643　MPa　and　an　elongation　of　22.7%　was　obtained　at　a　welding　speed　of　30　mm　s-1　and　the　laser　power　of　2200　w　in　CO2　laser　welding,　the　tensile　strength　of　laser　welded　joint　was　more　than　that　of　the　both　based　metals.　The　center　of　the　welding　seam　was　composed　of　slender　lath　martensite　with　a　few　small　white　pieces　of　ferrite.　The　microstructure　of　the　Heat　Affected　Zone　(HAZ)　on　the　DC52D+ZF45　side　was　smaller　than　that　of　the　HAZ　on　the　ASSAPH440　side,　and　its　mechanical　properties　were　superior.　The　highest　microhardness　was　obtained　at　the　center　of　the　cross　section　of　the　welding　seam,　and　the　microhardness　of　the　welding　seam　on　the　DC52D+ZF45　side　was　higher　than　that　of　the　welding　seam　on　the　ASSAPH440　side.　The　tensile　fracture　appeared　at　the　base　metal　of　DC52D+ZF45　steel　as　a　result　of　the　strength　of　ASSAPH440　was　more　than　that　of　DC52D+ZF45.　The　performance　of　the　laser　welded　joint　met　the　technical　requirements　of　automobile　manufacturing　engineering.　©　2020　The　Author(s).　Published　by　IOP　Publishing　Ltd.