Monopile, tripod and jacket structures are the most popular foundations adopted in offshore wind farms in Europe. Piles with diameters mostly larger than 2 m are usually installed for these foundations. More than 500 offshore wind turbines shall be installed in the Taiwan Strait in the next 20 years. However, due to limited pile driving capacity of the marine engineering industry in Taiwan, the pile group foundation with pile diameters of maximum D = 1.6 m is considered as foundation for offshore wind turbines and a research platform. This paper aims to investigate the behavior of multi-pile-soil system under monotonic lateral load. A three-dimensional finite element model with non-linear material behavior of the subsoil was established. The deformation responses of a pile group platform foundation calculated with FEM under monotonic lateral load are compared with the results calculated with a simplified approach based on the p-y-curves method. The bearing behavior of the pile group platform foundation cannot adequately considered by the simplified approach. To evaluate the suitability of group pile platform foundation, the deformation responses of a typical monopile are considered as reference values. The investigated pile group foundation is more flexible than the monopile, i.e the lateral deformations of the piles are much larger than the deformation of the monopile. However, due to the great stiffness of the platform plate the rotation of the platform is within the usual tolerance for offshore wind turbines and even smaller than the inclination of monopile.