Abstract: Large-scale physical model tests are carried out to study the mechanical characteristics of high-rise platform pile groups subjected to cyclic lateral loads such as wave, tidewater and wind, etc. They are conducted in silts, which consist of nine steel-pipes in a closely-spaced arrangement. The response of pile groups and its variation under cyclic loading conditions are discussed. The results indicate that the cyclic loading produces plastic deformation within soil around piles. The lateral stiffness of pile-soil system decreases with cycling, and the lateral load carried by each pile is redistributed during repeated loading. The previous cyclic loading influences the stiffness of piles in the next loading stages. The effect induced by the cyclic loading is more important for group-pile than a single pile, which can be estimated by a multiplier based on the p-y curve method. Finally, a comparison between the calculated results and those obtained by other different methods is presented.