The invention relates to the technical field of construction, in particular to an integrated construction method related to an in-water steel pipe pile establishing platform. According to the method, when cushion cap lower silt layer thickness reaches about 30 m, a large non-pile collar beam foundation between cushion caps and an in-water steel platform supporting system are completed by one-time construction, and the problem that during cushion cap collar beam foundation and steel platform supporting system independent construction, a steel pipe pile is inserted and stricken repeatedly, and on-water workload is high is solved. The method comprises the steps that the steel pipe pile is inserted and stricken below the cushion cap collar beam, the steel platform is established, and pile foundation construction is carried out; the steel platform supporting system on the upper portions of the cushion caps is detached, a steel cofferdam is arranged, cushion cap collar beam inner steel pipe pile spare parts are cut off, integral pile caps are cast, and the cushion cap collar beam is cast. Compared with the prior art, the integrated construction method has the advantages that integration construction is carried out under the foundation of the steel platform and the foundation of the cushion cap collar beam, steel platform materials are saved, construction cost is saved, steel pipe pile repeated using is carried out, the workload of on-water working is lowered, and the construction cycle is shortened.