Abstract: To investigate the stability of SMW (Soil Mixing Wall) method piles in deep foundation pit support within the mud-sand composite stratum in Foshan, this study adopts a theoretical calculation approach, taking a public cultural venue foundation pit in Nanhai District, Foshan City, as the engineering case. A mechanical calculation model of the SMW pile support structure in the mud-sand composite stratum was established. Through theoretical calculations, the ground settlement around the pit and the displacement of the supporting structure induced by excavation were analyzed, and the calculation results were systematically compared with on-site monitoring data. Both theoretical and monitoring results demonstrate that: (1) SMW method piles perform effectively in supporting deep foundation pits within the mud-sand composite stratum in Foshan; (2) By optimizing the mix proportion of cement-soil mixing piles and the layout parameters of steel beams, SMW method piles successfully form a dual-function composite support system integrating structural stiffness and water-sealing capabilities; (3) Compared to traditional support techniques, SMW method piles demonstrate significant comprehensive advantages in safety, economy, environmental friendliness, and efficiency in composite formations of silt sand layers. The findings provide valuable references for similar engineering projects and advance the development of relevant technologies.