Abstract: Wet joints of a main girder were usually structural weak parts in a prestressed concrete cable-stayed bridge. In order to reveal the failure mechanism of wet joints, a construction stage analysis model for Yonghe Bridge in Tianjin was established, and then concrete stresses of the wet joint between the closure segment of main span and one of its neighboring precast segments were calculated. Using this model, the influences of the overload effect of living loads, relaxation of stay cables, concrete shrinkage and creep to the concrete stress state of wet joints were analyzed. Thereafter, some configuration defects at wet joints were elucidated. Studies showed that overloading for a long service period was the most important factor for failure of wet joints. Moreover, some factors in service, such as the stay cable relaxation or concrete shrinkage and creep, could also contribute to the failure. In addition, the position of wet joints in bridge spans, the layout of prestressed steels of the closure segment, the treatment of joint surface between new and old concrete, and the reinforcement ratio at joints were the internal factors of failure. Based on these conclusions, some suggestions were provided in terms of design, construction, and maintenance.