Abstract: Based on the fundamental equations of staticmagnetic field and the principle of finite element method, a new combined boundary element-finite element method for the computation of rotational symmetrical magnetic field with unsaturated iron medium is studied and a program for the design of electromagnetic focusing imaging systems drawn up. The methdd shows that the question of closed boundary, when using finite element method only can now be settled. It also shown . that the new method is very efficient for the engineering design of imaging systems, as well as for ordinary magnetic lenses.