The pile core and cap of high pile wharf are the key structures of pile top connection,and the traditional cast-in-place construction on water usually faces operational difficulties and construction quality problems.The prefabricated pile core and cap structure is changed from cast-in-place to prefabricated in factory,and the pile top structure is formed by grouting material and steel pipe piles,which avoids the influence of hydrological conditions on its construction.In this paper,the failure mode and grouting material ratio of precast pile core and cap structure are studied by physical experimental.The results show that the interface between grouting material and precast pile core of pile top structure is immobile under vertical load,only the relative displacement between grouting material and steel pipe is generated,and the interface bond behavior between grouting material and inner wall of steel pipe is relatively weak.The bond strength between UHPC grouting material and steel pipe decreases with the incorporation of steel fiber and increases with the incorporation of expansion agent.The combination of 0.08% plastic expansion agent and 12% national standard II expansion agent is the optimal ratio.The interfacial bond strength shows an increasing trend within 28 days and tends to be stable after 28 days.