Abstract: With the deepening of the western development strategy,a large number of high-fill projects have emerged in the northwest loess region. It is generally believed that the excavation-filling combination area is considered to have poor building suitability,leading to almost a blank in the research on the foundation treatment of high-rise buildings in the excavation-filling combination area in China. This article analyzes the interaction relationship between pile-soil-water in the excavation filling joint area of loess high fill sites through the largest immersion experiment in the northwest region. It was found that the surface water seepage is the fastest along the excavation-filling interface,and the filling area is the slowest. The original loess mainly infiltrates vertically,while the reshaped loess mainly infiltrates horizontally. It was found that there is a neutral point in the relative vertical displacement of piles and soil near the excavation-filling interface. The filling area is filled with friction piles,and the excavation-filling combination area is end-bearing piles. Suggestions have been put forward for land planning,foundation treatment,structural design,and other aspects applicable to the excavation-filling combination area.