The seismic response of the structure is nonstationary random vibration because earthquake excitation is nonstationary random vibration. Calculating method for the statistical characteristics of such a nonstationary response is complicated. The mean square value of the response is usually used to evaluate the statistical characteristics of random response. Integral of the mean square value of the response corresponds to total energy of the response. In this paper, a simplified calculation method to obtain integral of the mean square value of the nonsatationary response is proposed. In this method, the mean square value of the stationary response is used. As an earthquake excitation, nonstationary filtered white noise is used considering the dynamic characteristics of the ground. Integrals of the mean square value of the nonstationary random response are calculated for various values of parameters. It is found that the proposed method gives exact values of integral of the mean square value of the nonstationary random response.