Abstract:he main span of Xihoumen Suspension Bridge is 1 650 m,and its main tower(bridge foundation) with height above 200 m lies on an island in the sea. Stratum near the bridge foundation is rhyolite porphyry in late Jurassic period. A little of slope eluvium exists on the top of the mountain,which is 200 m long and 80 m wide,and its all sides face to sea. The integrality of rock mass of the mountain is relatively poor because of the effect of some faults and other structural fissures. Obviously,the stability of the bridge foundation slope considering the united effect of large span and high tower,especially the repeated additional effect of typhoon,is a key problem related that whether the bridge project is tenable. Combining the design place of the bridge foundation,considering engineering load effect,it is found that the position where destabilization will happen most easily is the south slope;and the possibility that the large-scale destabilization happens in other positions of the slope is small. Based on the field geological survey,the boundary conditions controlling the stability of south slope are found. Systematic analysis of the slope stability is conducted under the integrated effects of top structure loads,especially the wind load through many methods.