Five　kinds　of　B-bearing　high　speed　steel　roll　alloy　was　designed　and　prepared.　The　microstructure　and　properties　of　B-bearing　high　speed　steel　with　different　composition　and　temper-treatment　process　were　investigated　by　the　way　of　optical　microscopy　(OM)　,　scanning　electron　microscopy　(SEM)　,　X-ray　diffraction　(XRD)　and　hardness　measurement　,　impact　test　and　abrasion　test.　The　results　show　that　as-cast　microstructure　of　B-bearing　high　speed　steel　consists　of　martensite　matrix,　retained　austenite　and　borocarbide.　Hardness　of　as-cast　B-bearing　high　speed　steel　excels　HRC　64.　The　eutectic　borocarbide　is　distributed　in　a　network　along　the　grain　boundary.　After　RE-Mg-Ti　compound　modification,　the　networks　of　borocarbide　is　broken.　The　hardness　of　B-bearing　high　speed　steel　roll　alloy　gradually　decreases　with　the　increase　of　tempering　temperature.　Under　the　same　conditions,　the　impact　toughness　of　unmodified　B-bearing　high　speed　steel　roll　alloy　is　slightly　lower　than　that　of　modified　alloy.　The　wear　resistance　of　modified　B-bearing　high　speed　steel　roll　alloy　is　greater　than　that　of　high　carbon　high　vanadium　high　speed　steel　roll　alloy.