The utility model relates to a cofferdam of a deep-water single-wall steel lifting box. The steel lifting box comprises an enclosing system, an inner support system and a bearing system, wherein the bearing system consists of a lifting bracket, an upper cross beam, a lower cross beam and a lifting rod; the lifting bracket is welded at the inner side of a side plate; the upper cross beam is positioned at the top surface of a longitudinal steel protective drum and is connected with the lifting bracket by the lifting rod; and the lower cross beam is welded on a pile top position and is parallel to the upper cross beam. Due to adoption of the cofferdam, the technical problems that for the traditional cofferdam, the quality of bottom sealing concrete is hard to guarantee, and water seepage and water leakage are easy to occur are solved. The cofferdam can be widely applied in construction of pile bearing platforms and piers in deep water areas.