For　some　pig　iron　used　to　produce　gray　castings　has　microelement　As,　a　great　deal　of　cracks　or　microcracks　are　prone　to　forming,　which　results　in　reject　of　castings.　Iron　melts　with　different　As　contents　were　smelted　by　using　mid-frequency　coreless　induction　furnace　and　test　samples　were　prepared.　The　effects　of　As　on　the　graphite　morphology　and　microstructure　of　castings　were　investigated　by　using　metallographic　microscope　(XTB-1).　WES　hydraulic　universal　test　machine　was　applied　to　test　the　tensile　and　bend　strength.　Castability　of　the　samples　was　also　studied.　The　result　shows　that　As　can　promote　forming　of　supercooling　graphite　and　pearlite,　but　excessive　As　resulted　in　the　formation　of　network　carbide,　aggravated　the　segregation　of　phosphide　eutectic　and　enhanced　the　chill　depth　and　shrinkage　rate　of　castings,　thereby　resulted　in　serious　stress　concentration　and　hot　tearing,　which　are　the　main　reasons　of　cracks　forming.　In　the　practical　production,　the　As　content　of　cast　iron　must　be　controlled　less　than　0.010%,　and　the　mechanical　property　can　be　increased　by　improving　the　metallographic　structure　of　casting　by　some　measures,　such　as　inoculation.