The　present　work　studied　the　effects　of　different　modification　treatments　on　the　microstructure　and　mechanical　properties　of　hypereutectic　high　chromium　cast　iron　containing　about　35　wt%　chromium　and　4.0　wt%　carbon.　It　was　found　that　the　primary　carbides　in　the　hypereutectic　high　chromium　cast　iron　were　all　refined　to　different　levels　after　different　modification　treatments.　Among　them,　the　best　result　was　obtained　by　adding　0.6　wt　%　rare　earth　magnesium,　and　its　average　carbide　diameters　was　43　mu　m,　which　is　almost　half　of　the　unmodified　specimen.　After　modification,　the　mechanical　properties　have　been　improved,　and　the　refinement　of　primary　carbides　can　greatly　improve　its　impact　toughness.　The　impact　toughness　of　the　specimen　modified　by　adding　0.6　wt　%　rare　earth　magnesium　was　the　largest,　reaching　7.0　J　cm(-2),　and　the　impact　toughness　of　un-modification　specimen　was　the　worst,　only　4.5　J　cm(-2).　The　refining　of　primary　carbides　does　not　have　much　effect　on　the　hardness.　The　hardness　of　the　sample　with　0.6　wt　%　rare　earth　magnesium　and　0.3　wt　%　TiBAl　is　the　highest,　and　its　value　is　58.0　HRC.　The　wear　resistance　increases　with　the　refinement　of　primary　carbides.