Abstract: In this paper, the currently used equivalent linear methods for calculating seismic responses of nonlinear soil structures are briefly summarized and some improvements are made. A new approach, the probabilstic average approach, is proposed. A numerical example is presented in detail by using all kinds of equivalent linear methods, including the proposed onet Monte-Carlo simulation method is appeied to examine the results. It is found that the concept of proposed method is more clear and the precision is higher than other approaches.