In　order　to　find　the　crack　reason　of　H700X300　H-beam　rolled　in　air-cooling　conditions,　finite　element　analysis　has　been　used　to　study　the　cutting　process.　Find　that　the　R　position　existed　serious　stress　collection　when　cutting　to　the　central　of　the　web　in　the　cutting　process.　The　stress　is　three-dimensional　stress,　and　each　is　tensile　stress.　It　is　accord　with　the　Q235　steel　brittle　fracture　law.　So　the　conclusion　can　be　draw,　the　reason　of　H700X300　H-beam　occur　cut　fracture　is　for　exist　crack,　stomata　and　other　defects　in　the　stress　collection　position.　The　experiment　testify　the　conclusion