The invention discloses a construction method for a special-shaped steel cofferdam, which comprises the following steps of: measurement and positioning, erection of a steel pipe pile bracket, installation of a steel cofferdam laying fixation device, assembly, heightening and laying of the steel cofferdam, deviation correction and positioning of the steel cofferdam, bottom seal in a compartment and the steel cofferdam, disassembly of the steel cofferdam steel pipe pile bracket, erection of a pile foundation borehole platform, positioning and installation of a steel casing (24), final bottom seal, drilling and pile formation, disassembly of the pile foundation borehole platform, water pumping from the steel cofferdam, chiseling of pile head concrete, construction of a bearing platform and apier body, cutting and reclamation of the steel cofferdam, and clearing of the river, wherein the assembly process of the steel cofferdam comprises assembly of a first section, namely a bottom section (6), and the shape of the assembled special-shaped bottom section can be tightly combined with the river. The method is suitable for foundation construction of a deepwater bridge pier without a covering layer and with complex terrain on the riverbed, saves the work amount of blasting and chiseling on the bottom rock layer of the riverbed, is easy for next bottom sealing construction, and can save the bottom sealing concrete number and the work amount of processing the steel cofferdam.