Abstract: Due to their unique ecological functions and historical and cultural heritage, ancient and famous trees need to be protected as a priority in the process of urban construction. However, the soil disturbance and soil erosion caused by deep excavation construction can have serious adverse effects on the growth environment of ancient trees, so it is urgent to study an effective in-situ protection plan for ancient trees. This article takes a 235 year old ancient autumn maple tree as the protected object, designs a cantilevered octagonal interlocking pile support structure, and uses meat vegetable piles arranged in a staggered interlocking manner to form a closed water stop system; Paired with double-layer staggered square steel pipe internal support, the overall stability is enhanced through crown beam connection. Simultaneously develop a complete construction process including bite pile construction, crown beam pouring, support installation, ancient tree rejuvenation, and support removal, and strictly control the positioning accuracy and verticality of the pile body. This scheme effectively resists the soil stress generated by deep foundation pit construction, reduces soil disturbance and soil erosion, controls pile top displacement within a safe range, and ensures the stability and normal growth metabolism of ancient tree roots. It has important academic value and practical significance.