The in-line measurement on no-load magnetic field of mold electromagnetic stirrer for 350 mm x 470 mm bloom casting has been carried out to get distribution rule of magnetic induction in mold. Based on magnetic field measured results the electromagnetic force at solidifying front and liquid rotational velocity are calculated and the effect of electromagnetic stirring parameters on liquid rotational velocity is analyzed to define the range of stirring current and frequency. The results of commercial casting of steel 42CrMo show that as mold stirring current is 150 A with frequency 2. 5 Hz

the maximum deviation of carbon content at cross section of bloom is ±0. 01%

the macro-segregation band of bloom is basically e- laminated and the internal quality of bloom improves obviously.