The invention relates to the field of offshore wind power mechanisms and aims to provide an offshore wind turbine tower foundation structure and an installation method. The offshore wind turbine tower foundation structure comprises an offshore jacket and a column pile component, wherein the offshore jacket comprises one or more cylinders arranged on the bottom, the column pipe component comprises one or more parallel column piles, the top of the column pile component is arranged in the cylinders, the portions, in the cylinders, of the column piles are connected through connectors, and the cylinders are grouted to enable the column pile component to be connected with the cylinders. The offshore wind turbine tower foundation structure has the advantages that the column piles can be small-diameter steel pipe piles, the multiple column piles are mutually connected through the connectors and connected with a sleeve on the bottom of a main conduit of the offshore jacket through grouting, so that a grid structure is formed by the column piles, structure inertia moment is increased, the overall rigidity and horizontal bearing capacity of the structure are improved, horizontal displacement of the bodies of the column piles is reduced, and the anti-topple capacity of a foundation is improved.