In the present work, the effect of electromagnetic field on the microstructure and the alloying agent distribution was investigated. Tin element was shown to have the tendency to be inversely segregated on the surface of tin bronze. The microstructures of the continuous cast tin bronze plates are coarse and inhomogeneous. The factory test parameters were determined according the simulated data. The flow behavior of the mercury to be stirred as well as the relations between the microstructure of plate blanks and the current parameters were analyzed. With an appropriate electromagnetic stirring, the inverse segregation of tin for C51900 alloy plant blank was improved by 80%, and the microstructure was refined from about 10mm to 1~3mm in grain size.