Abstract: Due to the ever-changing and complex geological conditions, the design of foundation pit support must vary from place to place. In areas with rich water and sandy soil, improper support systems can easily lead to water seepage and leakage in foundation pits, resulting in safety hazards and affecting construction safety, quality, and progress. In traditional construction, underground continuous walls, cast-in-place pile rows, and waterproof curtains are often used for support construction, but this method has high cost and slow construction speed. Therefore, this article studies the comprehensive support system and construction technology using mixing piles and rotary jet grouting piles between pipe piles. Through numerical simulation, on-site monitoring, and comparative analysis using MADIS/GTS software, the following conclusions are drawn: considering the simulation analysis and on-site monitoring of groundwater, this system can effectively isolate groundwater, with small water level drop and good waterproof effect of the waterproof curtain. The most unfavorable displacement of the simulated crown beam is 12.50 mm, and the maximum displacement monitored on site is 12.70 mm. The values of the two are similar, safe and reliable. At the same time, compared with the construction of the cast-in-place pile row crown beam, it can effectively eliminate the noise and dust pollution caused by breaking the pile head. The maximum horizontal displacement of deep layers at 2.5 m, 5.0 m, and 7.5 m of the excavation surface was measured to be 9.22 mm, 10.30 mm, and 9.91 mm, respectively. The simulated values above the excavation surface can effectively cover the measured values. Compared with underground continuous walls, cast-in-place pile rows, and waterproof curtain support systems, this construction system has the advantages of factory prefabrication, no maintenance required, half construction period, and low comprehensive cost. The construction period is shortened by half, and the comprehensive cost is saved by half. This system is suitable for water rich sandy soil areas and has significant economic and social benefits. It is worth promoting and applying in similar projects in similar areas.