The construction difficulty and safety risks of minimal-distance shield tunnels are high, which affects the safety of the shield structure and surrounding environment. Based on a newly built shield tunnel in Shenzhen, a numerical analysis model is established using finite element software FLAC 3D to study the deformation mechanism and impact of isolation piles on the construction of small-clearance shield tunnels in composite strata. Sensitivity analysis is conducted on such factors as different pile length, pile diameter, and pile spacing. Suggestions for shield construction in composite strata are proposed. The results show that: The isolation piles can effectively reduce the vertical displacement in the shield tunnel, with relatively little impact on the horizontal displacement; The maximum vertical displacement of the shield tunnel is approximately inversely proportional to the length of the isolation piles, nonlinearly decreases with the diameter of the isolation piles, and nonlinearly varies with the spacing between the isolation piles; It is reasonable to take the diameter of the isolation piles in this project as 1m , and it is recommended to appropriately increase the spacing between the isolation piles to reduce engineering costs.