The engineering geological conditions of a newly constructed pump station are complex, with the maximum excavation depth of the foundation pit reaching 7.60 m to the pile cap. The site contains thick layers of miscellaneous fill and silt, as well as significant variations in groundwater levels and developed karst features. Therefore, the selection of the support scheme is crucial for controlling the project cost. To optimize the support scheme, a technical and economic comparative analysis of the SMW method, underground diaphragm walls, and the composite support scheme of "bored cast-in-place piles + high-pressure jet grouting piles" is conducted. Engineering practice has demonstrated that this composite support system has successfully addressed the construction challenges in karst areas, combining the support stiffness of bored cast-in-place piles with the watertight barrier effect of high-pressure jet grouting piles. The results can provide practical reference for the selection of support types, scheme comparison, and construction measures for deep foundation pits at pump stations under similar adverse geological conditions.