Scaled boundary finite element method (SBFEM) is used to analysis and calculate electromagnetic field problems. SBFEM equation and discrete format of irrotational magnetic fields are derived with weighted residual method. Solving method of inside common node on public edge of adjacent sub-domain is shown. A typical example that has analytical solution of electromagnetic field is used for comparative analysis, which verifies discrete format correctness and feasibility of the method. Foundation for method applications in electromagnetic field calculation is made.