The tested H section steel Q235 (/% : 0.06C

0.30Si

1.60Mn

0.010P

0.003S

0.025Mo

0.40Ni

0.017Ti

0.15Cu) is produced by 80 t LD-LF-feeding silicon-calcium wire-28 t tundish-430 mm x 300 mm x 85 mm H section CC bloom-hot rolling process. Due to the longitudinal crack easily occurred on surface of H section steel bloom

based on real process parameters of through type double submerged nozzle for H section casting bloom

a mathematical model is established and the calculation of distribution of flow field and temperature field in mold is carried out by using fluid finite element simulation software CFD. It is obtained that with using through type double submerged nozzle the impact depth in pool is large that is unfavorable to inclusions floating off； and the liquid surface can't get enough heat supply led to bloom shell more earlier solidification and unfavorable to slag melting. The results of numerical simulation show that as casting by using modified three side nozzle

the unfavorable factors with using through nozzle are avoided

the distribution of flow field and temperature field is reasonable

and the possibility of bleeding trouble and occurrence of crack decreases.