In this paper, a scheme to stabilize multiple-region finite-difference time-domain (MR-FDTD) method is proposed. This method utilizes a polynomial approximation to equivalent electric and magnetic currents on an equivalence surface. If analysis domains are narrow in MR-FDTD method, a reflected wave from an absorbing boundary causes not good influence into MR-FDTD method. It was confirmed that the method removes a higher frequency noise. Therefore, the method provides stable analysis results.