The technique of surface impedance boundary condition (SIBC) can avoid calculating the fields inside conductor and the results have been proved valid under certain conditions. More recently, some authors studied the surface impedance of a lossy dielectric with exponential approximation (J.G. Maloney and G.S. Smith, IEEE Trans. Antennas Propagat., vol. 40, pp. 38-48, 1992), with a first-order rational approximation series expanding (K.S. Oh and I.E. Schutt-Aine, ibid., vol. 43, no. 7, pp. 660-666, 1995), or with a higher order SIBC (M.K. Karkkainen and S.A. Tretyakov, ibid., vol. 51, pp. 2448-2455, 2003) for a time domain model. Their obtaining is in good agreement with exact result for a large value of conductivity, normal incident angle, etc. However, the content of their research contains only unilateralism. This investigation is performed a full time-domain implementation of the SIBC model by expanding the exact operational surface impedance accompanying a suitable rational approximation. The algorithm is valid for problems in areas in which we are interested such as small conductivity, incident angle, and polarizations.