The invention discloses a diagonal-web-member-free fabricated steel cofferdam structure. The structure is cylindrical and comprises a cofferdam framework formed by assembling a plurality of assembly units; each assembly unit comprises double crossed units or double T-shaped units, each double crossed unit or T-shaped unit consists of horizontal chord members on inner and outer sides, connection rods and vertical chord members; each unit is connected with the middle parts of the horizontal chord members and the vertical chord members through bolts so as to form the cofferdam framework; and inner and outer wall plates are connected with the framework by hook bolts so as to form the steel cofferdam structure. The diagonal-web-member-free fabricated steel cofferdam structure can be manufactured to have a circular or curved cylindrical cofferdam structure which is light and firm; and the welding process for the diagonal-web-member-free fabricated steel cofferdam structure is mainly finished in a factory, and manufacturing accuracy and quality can be improved; each grid has a diagonal-web-member-free structure, so the steel using amount is reduced, and operation between grids can be performed conveniently; and the cofferdam structure is suitable for bridge foundations and various underwater engineering construction, and can separate water temporarily.