The pile group efficiency under horizontal load is an important parameter that affects the horizontal resistance of group piles foundation. The constant stress diffusion angle of geotechnical material is assumed in this paper while the influence of geotechnical material parameters on the interference effect between adjacent piles is considered, and the pile group effect coefficients under different arrangements are re-derived on the basis of the principle of elastic superposition. The pile group effect coefficient is used to solve the pile group efficiency formula in the form of 1×2, 2×2, and 3×3 layout. And this article analyzes the influence of pile spacing to pile diameter ratio, elastic modulus and Poisson’s ratio on the efficiency of pile groups through finite element analysis. It is found that the pile spacing to pile diameter ratio and elastic modulus have significant effects on pile group efficiency, while Poisson’s ratio has little effect. Finally, the reliability of formula solution in solving pile group efficiency is verified by comparing the finite element numerical solution and formula solution of pile group efficiency.