In order to overcome the problem of high storage requirement and slow convergence rate of indirect bound-ary element method

a new indirect boundary element method with a low storage requirement is proposed. The coeffi-cients of the indirect boundary element equations are obtained by the Galerkin approach

and the iterative procedureof the equations is constructed according to the difference of the degree of physical coupling. For the coefficients cor-responding to elements with distant spatial distances

they are directly calculated in the iteration. Since these coeffi-cients are not stored

the storage of the system of equations can be reduced from O（N2）to O（N）. The method is ap-plied to the capacitance calculation of the bounded wave simulation generator. Numerical examples show that the pro-posed method can effectively improve the design efficiency and accuracy of impedance matching. In theory

themethod in this paper is essentially an application of pre-conditional technology based on physical coupling

so it canbe generalized to the case where the numerical calculation of electromagnetic field involves full-scale solution.