The model of finite differential method for solutes micro-segregation during solidification of steel has been established by analysis on representative regular hexagonal dendrite structure micro-segregation model combined with applied steel grades. Non-equilibrium solidus lines calculated by established model coincide with the related experimental data published by Jemkontoret. The application of heat transfer calculating model for 280 mm x380 mm casting bloom of 0. 20C steel

0. 45C steel and U71Mn steel show that the length of liquid-solid region at center of bloom calculated by non-equilibrium solidus is longer than that calculated by equilibrium solidus and it increases with increasing carbon content in steel ； and the revised solidification parameters and established model are more precise to reflect the solidification process.