Abstract: Based on the Unit Cells theory and the shear displacement theory, the pile-to-pile elastic coupling principle of mirroring image method was introduced, and shear displacement cell mode was built for analyzing the load transfer of piles in large pile group. The generalized shear displacement analytical expression was deduced by introducing the generalized shear displacement concept, which can be explained as a superposition of shear displacement and relative slippage of pile-soil interface. The iterative solving method was presented based on the pile tip displacement coordination condition. An case analysis reveals the effects of sparse piles space and the load level on the settlement-reducing property of sparse pile foundation. The load-displacement transfer characteristics of sparse piles and foundation are described. The contact mechanism of the sparse-pile foundation working property of the pile top relative displacement and the stiffness of the pile end bearing layer is explained. The validity of the model and the flexibility of the algorithm are also verified.