To provide a waterproof sheet, a manufacturing method thereof and a waterproofing method without imparting an adverse effect to environment through benefits such as the short term of works, the simple and economical application, and no secondary environment pollution.

The method for waterproofing a recessed inner face of an underground structure utilizing a natural ground comprises a step of compacting the surface of a natural ground recessed part by rolling, a step of directly laying a netlike member 32 on the surface of the recessed part 31 after the rolled compaction and a step of spraying a polyurethane resin 35 on the surface of the netlike member 32 so as to form a fixed thickness of the polyurethane resin. An abnormality of the polyurethane resin layer, and the like, are detected by using a metal wire 34, as a sensor of X, Y directions which is provided in rectangular arrangement inside the polyurethane resin layer 35. Subsequently, a damaged part of the waterproofing sheet is repaired by charging a polyurethane resin A liquid and a curing agent B liquid to the damaged point by the pinpoint injection through a mixing nozzle.