Abstract: Based on the riverside foundation pit project at the Agricultural and Forestry University Station of Fuzhou Metro Line 5,this study systematically investigated the mechanical behavior of a riverside foundation pit under complex geological conditions through model testing, numerical simulation, and field monitoring. The following conclusions were drawn: The horizontal displacement of the retaining wall increased progressively with excavation depth, exhibiting an"arch"-shaped distribution along the wall. Owing to complex geological conditions, the displacement on the mountain side exceeded that on the riverside, resulting in an overall deviation of the foundation pit toward the Min River. Axial forces in all five levels of bracing increased gradually during excavation. The third concrete brace, characterized by high stiffness and located in the zone of maximum wall deformation, developed significantly greater axial force than the other four braces, playing a critical role in the support system. Earth pressure on the retaining wall transitioned gradually from the at-rest state to the active state during excavation. The variations in earth pressure increment were generally consistent on both the mountain and river sides. These findings provide a valuable reference for the design and construction of similar riverside foundation pits under complex geological conditions.