This paper innovatively provides a coherence function model,specially adapted for water-covered canyon-hill composite topography and for simulating the multi-support seismic motions.First,a new coherence function model considering the soil filtering effect and vertical distance is proposed and derived.The characteristics of coherence and physical meaning of the proposed model are further investigated and summarized.Then,the multi-support underground seismic motions are generated by decomposing the underground power spectral density matrix,which is formed by combining the coherence function based on the derived model with the transfer function.Subsequently,the reasonability and rationality of the simulated results are verified by comparing the simulated power spectrum and the coherence function to the theoretical ones.Finally,the influence of the presented coherence function model on the differential effect of multi-support seismic motions and the dynamic response of a continuous rigid frame bridge is specially analyzed,respectively.The results show that the coherence among the simulated variable seismic motions is relatively reduced,but the variability of seismic motions at each foundation is increased,which leads to the enlargement of the structural responses.