To provide an economical cofferdam structure and cofferdam method.

This cofferdam structure 18 is provided with a plurality of separably connected precast panels 20 and installed to surround an underwater structure such as a bridge foundation. The panel 20 is composed of a standard panel 22 and a deformed panel 24. The panel 22 is formed in linear rectangular shape having predetermined width and length, and the panel 24 is formed in bent plate shape with the plane shape bent in a dog-legged-shape. A parallel part of the structure 18 has five panels 22 connected to one another. A polygonal part is formed by connecting four deformed panels 24 and three standard panels 22 alternately. Bolts and nuts 32 are used for connecting the respective panels 22, 24, and the respective panels 22, 24 are separably connected by the fastening structure of the bolts and nuts 32.