Abstract: In the floodplain area of mountainous areas, the upper soil layer is relatively thin and low in strength, while the underlying bedrock has high strength, thick thickness and stable distribution. Excavation of deep foundation pits under such geological conditions, when the surrounding environment of the foundation pit is complicated and the space for grading is limited, it is difficult and expensive to use the traditional pile row system to construct; and the supporting system of "hanging foot pile" with shallow embedded depth often loses its applicability due to the blocking of anchor pulling in the middle and upper part of the pile. In order to solve the above problems, combining the experience of deep foundation pit support combined with soil and rock in northwest Hubei, a design and construction method of top-down pier type retaining wall support is proposed. The engineering practice shows that the calculation theory of the top-down pier type retaining wall is clear, and it has obvious advantages such as convenient construction and economical cost. Relevant results can provide important technical reference for similar deep foundation pit engineering.