Abstract: Complex analysis is an effective finite element method to simulate the dynamic response of rock soil mass to earthquake. By using complex modulus to format the stiffness matrix, the damping ratio is irrelevant to the frequency, then the properties of rockmass can be simulated rationally. In this paper, a case about a mountain tunnel along Chuanzhang Highway is used to analysis the characteristics of dynamic response of rock soil mass to earthquake, and the correlation of the tunnel depth with the seismic intensity is also discussed.