In　this　study,　a　CALPHAD-coupled　finite　element　model　was　established　to　reveal　the　formation　mechanism　of　hot　cracks　(including　liquation　and　solidification　cracks)　in　the　dissimilar　6061/7075　resistance　spot　welding　joints.　The　partially　melting　zone　(PMZ)　and　the　fusion　zone　solidified　under　tension　during　the　cooling　stage.　When　the　composition　of　the　local　area　is　susceptible　to　hot　tearing,　crack　initiation　would　take　place.　This　can　be　revealed　by　the　CALPHAD-coupled　finite　element　model.　At　the　6061/nugget　interface,　the　PMZ　was　torn　apart　under　the　thermal　strain　to　form　cracks　which　are　perpendicular　to　the　nugget　border　(Type　I　liquation　cracks).　At　the　7075/nugget　interface,　the　PMZ　was　torn　apart　by　the　solidification　contraction　of　the　nugget　((fS)nugget　＞(fS)7075)　to　form　cracks　along　the　tangent　line　of　the　nugget　border　(Type　II　liquation　cracks).　The　calculation　of　the　divide　dT/d(fS)1/2　divide　index　shows　that　the　solidification　cracking　susceptibility　of　the　6061/7075　nugget　is　fairly　high.　The　metallographic　and　energy　dispersive　spectrometer　analysis　shows　that　the　Type　I　liquation　cracks　were　filled　by　the　liquid　within　the　nugget　while　the　Type　II　liquation　cracks　and　solidification　cracks　created　a　local　no-bonding　area.　The　Type　I　liquation　cracks　did　not　affect　the　mechanical　properties　of　the　joints　while　the　Type　II　liquation　cracks　deteriorated　the　mechanical　properties　of　the　joints.