Abstract: The solidification mathematical model was established by using GCr15 steel bloom as a research object. The effects of superheat，casting speed and cooling water on the solidification process of bloom were studied. By analyzing the center solid fraction and liquid core length of the bloom，the optimum F-EMS position was determined and the casting speed was optimized. The results showed that the superheat had the little effect on the solidification of the bloom. With the increase of the superheat，the surface temperature of the billet increased，the length of liquid core and the length of liquid zone increasd，while the length of two-phase zone decreased. The effect of casting speed was the largest，the surface temperature，the length of liquid core，the length of two-phase zone and the length of liquid zone were all increased with the increase of the casting speed. With the increase of the water ratio，the surface temperature of the billet and the length of the liquid core decreasd. When the water ratio was 0.29 L/kg，the superheat degree should be controlled at 15–35℃，the casting speed could be controlled in the range of 0.46–0.49 m/min，and the best casting speed was 0.48 m/min.

Key words: bloom, numerical simulation, center solid fraction, liquid core length