At present, there are still few studies on the overall deformation and mechanical characteristics of occlusive piles and non-rock-socketed piles with different rock-socketing depths in composite strata foundation pit engineering. In order to provide economic and reasonable support design suggestions, the foundation pit engineer of Yangcunjing Station of Nanjing Metro Line 5 is taken as an example, and the FLAC^3D numerical simulation software is used to analyze the foundation pit support effect of occlusive piles with different embedding depths, and the optimal rock-socketed depth is selected. The results show that: 1) In the composite strata, the maximum horizontal displacement, maximum support axial force, maximum bending moment and maximum displacement of soil outside the pit are inversely proportional to the embedding depth. However, with the increase of embedding depth, the variation range of each index gradually decreases, and it does not change after a certain depth. 2) Combined with the above variation law and site seepage conditions, considering the construction period and economic indicators, it is recommended that the optimal rock socketing depth should be 2 m. The results can provide a certain reference for the foundation pit support design of subway stations and urban high-rise buildings under similar geological engineering conditions in the Yangtze River Delta region.