Abstract: The superheating extent of liquid of 8620 gear steel (/% : 0. 18 〜0. 22C, 0. 17 ~ 0. 26Si, 0. 70 ~ 0.90Mn, ≤ 0.025P, 0.15 ~0.23S, 0.40 ~ 0.60Cr, 0.40 ~0.70Ni, 0.15 〜0.25Mo) for casting 300 mm x 360 mm bloom is 20 ~30 ℃ and the casting speed is 0. 5 ~0. 6 m/min, and by bloom drilling analysis, pin-shooting test, original position analysis and bloom macrostructure analysis the effect of electromagnetic stirring parameters [ M-EMS (100 - 200) A, (2.0 ~ 2.2) Hz, F-EMS ( 150 ~ 200) A, 8 Hz] and secondary cooling water parameters (Ⅰ- zone 28 L/min, Ⅱ - zone 38 ~45.6 L/min and Ⅲ- zone 19. 2 ~24 L/min) on C and S segregation in bloom has been studied. With using optimized process parameters- secondary cooling water Ⅰ- zone 28 L/min, Ⅱ - zone 45.6 L/min and Ⅲ- zone 19.2 L/min, and electromagnetic stirring M-EMS 150 A, 2. 2 Hz, F-EMS 200 A, 8 Hz, the ratio casting bloom of 8620 series gear steel with segregation index 0.98 ~ 1.05 increases to 92.8% from original 30%.