In　order　to　find　the　influences　of　the　forced　water　cooling　time　on　the　microstructure　and　mechanical　properties　of　large　scale　Q235　H-beam,　finite　element　technology　together　with　theory　research　was　used　to　analyze　the　temperature-time　curves　of　H-beam　undergone　different　controlled　cooling　time　and　the　transformation　temperature　of　bainite　and　martensite　during　the　cooling　process.　The　results　showed　that　if　controlled　water　cooling　time　reached　12　s,　25%　flange　temperature　and　50%　web　temperature　reduced　to　below　the　critical　temperature　of　the　formation　of　ferrite　and　pearlite　in　a　very　short　time.　Therefore,　it　is　impossible　to　improve　the　performance　of　the　H-beam　products　through　extending　cooling　time　unlimitedly　in　controlled　rolling　and　cooling　technology.