The whole process of the numerical simulation of electromagnetic field in the liquid steel inside the soft-contacting billet mold is presented by FEM (Finite Element Method) and BEM (Boundary Element Method). Whitney edge element FEM based on tetrahedral elements, the discretization of H-Φ equation and boundary integration equation is mainly explained. By connecting FEM and BEM, it needs less work and time to the calculate the electromagnetic field. Numerical simulation program of three-dimensional electromagnetic field is exploited and the solution is proved to coincide with the fact.