Abstract: Due to the complex site conditions and seawater layer,the differences between offshore and onshore ground motions were significant.However,there was little research on sea-crossing bridges’ seismic performance under offshore ground motion.Initially,83 sets of offshore and onshore ground motion records were selected from the K-net in Japan,and the characteristics of offshore and onshore ground motion were analyzed.Subsequently,the selection suggestions of intensity measures (IMs) for the sea-crossing cable-stayed bridge under offshore ground motions were proposed based on the logarithmic regression analysis method.Finally,based on the response characteristics of various components,the fragility curves of various components under offshore and onshore ground motions were established.The damage characteristics of various components were studied under offshore and onshore ground motions.The results reveal that there are significant differences between offshore and onshore ground motion.Spectral acceleration of the fundamental period is a suitable parameter for analyzing the seismic fragility of sea-crossing cable-stayed bridges.Additionally,the probability of damage to the components of the sea-crossing cable-stayed bridge is significantly higher under offshore ground motion than under onshore ground motion.It is necessary to select the offshore ground motion to investigate the seismic performance of sea-crossing cable-stayed bridges.