To enhance the rigidity of walls to eliminate the timbering in excavation space and thus obtain a retional sheathing structure in a method for sheathing and coffering a ground to be excavated.

An outside wall 10 and an inside wall 11 are constructed, and, firstly, a fill part 2 is excavated and a reinforcing member 12 which connects the doble walls is attached, and, secondly, a space 1 to be excavated is excavated. The depth of excavation is so set as not exceeding the limit of free-standing of the inside wall 10, and the filled part 2 is excavated again, the reinforcing member 12 is attached between the walls, and the process is repeated to perform excavation to a predetermined depth.