Abstract: Based on Winkler's foundation model and compatibility condition of pile and surrounding soil, Two-stage Method is used for setting up horizontal displacement governing equation of a single pile. Pile-pile interactions and those between pile and surrounding soil can be achieved according to simplified Mindlin's equation. Then, governing equations for pile groups are obtained by combining points above. Comparisons are drawn between the observed results of centrifuge model tests and those computed by the studied method.