To provide a dewatering method capable of easily and quietly performing pumping pipe driving work performed to drain water in an excavating groove for laying a potable/sewage water pipe.

Plural building frames 5 are provided in a ledge 4, plural earth retaining timbering 1 sticking face plates 3 between both building frames 5 facing to the earth retaining side are buried in the earth in a vertical row state, a sheet pile 15 is driven along the outside surface of the respective face plates 3, and earth in the timbering is excavated and removed to form an excavating groove 16. Then, plural pumping pipes 10 are driven at an interval in the vertical row direction toward the bottom surface of the excavating groove 16 from the inside of the timbering 1.