Abstract: With the introduction of the orthogonal expansion method and the pseudoexcitation method into the wave finite element analysis of complex site, a method with which the effect of the random site media on the coherency function of earthquake ground motion can be considered is proposed in this paper. The numerical examples show that the stochastic media of the site tends to reduce the lagged coherency function in the vicinity of the predominant frequency. This diminution phenomena resulted from the random site media should be considered in the coherency function research.