The invention provides a modular offshore converter station structure comprising an AC equipment module, a negative DC equipment module, a positive DC equipment module, main columns and column leg jacket bases. The negative DC equipment module and the positive DC equipment module are arranged symmetrically in the plane. The AC equipment module is positioned beside the negative DC equipment moduleand the positive DC equipment module in the plane. The plane geometric centers of the three modules form an isosceles triangle. The three modules are all three-layer main decks. A module connector isarranged at the outer axis between the decks of the module. Four main columns penetrating through each layer are symmetrically arranged about the plane center for the AC equipment module, the negativeDC equipment module and the positive DC equipment module and are connected with the four column leg jacket bases correspondingly arranged below. The modular offshore converter station structure has the advantages of maximizing the utilization rate of the three-dimensional space in the station, modularizing the AC and DC functions and omnidirectionally reducing the engineering cost.