Based on the research background of Suzhou Metro foundation pit engineering, combined with the actual engineering data and numerical simulation results, the relationship between the embedment ratio, stability and deformation of foundation pit was analyzed. Through numerical simulation, the position of the sliding surface and its relation with the embedment ratio and the depth of the foundation pit were clarified. The formula for determining the position of the sliding surface was derived, and the sliding radius of the circular sliding method was improved in the analysis of basal heave stability. The results show that the formula for determining the position of sliding surface can accurately predict the position of the sliding surface when Suzhou foundation pit fails by basal heave. On this basis, the embedment ratio determined by the improved calculation method of basal heave stability is in good agreement with the calculation results of the existing foundation bearing capacity method, which is 41% lower than the embedment ratio obtained by the traditional circular sliding method. The embedment ratio design of the subway foundation pit supporting structure is optimized.