According to the mechanics problem of ultra-large-diameter single-pile in offshore wind generator foundation, this paper simulates the mechanical characteristics of the single-pile by number software based on the practical engineering. Variation curves of pile length, pile wall thickness and displacement, stress, and data tables which displacement and stress are changed with the variation of pile wall thickness and increasing the flange are gained by computing results. The conclusions are obtained that the variation of pile length, pile wall thickness in certain range can affect pile displacement and stress, the local variation of pile wall thickness changes indistinctively displacement, but stress is changed observably, and the lateral displacement can be reduced effectively by increasing the flange in certain range under mud surface. The best underground length and thickness of the flange are given in order to provide the design basis for the practical engineering.