Low-cost dewatering method for foundation pit located in stratum containing runoff type interlayer water

The invention relates to the technical field of underground water control, and discloses a low-cost dewatering method for a foundation pit located in a runoff type interlayer water stratum, the whole foundation pit is no longer used as a whole needing dewatering, but a part, which can be really influenced by underground water in construction, in the foundation pit is regarded as a position needing dewatering after calculation, and the dewatering is completed. And the part is accurately subjected to precipitation. In the construction process, excavation is conducted under the condition of no rainfall, and when the periphery of the in-pit rainfall area is excavated in place and the in-pit rainfall area is flush with the periphery, a waterproof curtain is driven around the in-pit rainfall area. At the moment, the starting point of the waterproof curtain is not the ground surface but a deep underground position, so that the bottom of the waterproof curtain can be driven into an impervious layer in the deep positi