Abstract: In order to control the macro-segregation of gear steel,the chemical analysis and original position analyzer were applied on carbon distribution of billets in cross section.The superheat,casting speed,electromagnetic stirring and flowrate of secondary cooling testes had been performed and the optimal casting parameters were determined.The test results show that superheat range should be controlled at 20 ℃±5 ℃ and casting speed should beat 1.30 m/min.The current intensity of M-EMS and F-EMS should be 250 A and 50 A respectively.The flowrate of secondary cooling should be 0.41 L/kg.These parameters were benefit to the macro segregation control.The industrial results indicated that carbon segregation indexes of billets in cross section were 0.94 to 1.05 and hardness variation of bar at cross section were at ±10 HV range.