The invention provides a decompression type blocking method for a foundation pit dewatering well. The method includes the steps of step 1, sleeving a waterproof casing pipe outside a dewatering well pipe and carrying out reinforcement and embedment, step 2, embedding the waterproof casing pipe and pouring the waterproof casing pipe into foundation base plate concrete, step 3, cutting off unnecessary well pipes on the base plate surface after basement base plate concrete reaches a certain strength, inserting one drainage shock tube into the lower portion of the well pipes, and enabling the top end of the drainage shock tube to be communicated with a water conduit, step 4, shutting in the well, lifting a water pump out, then filling well shut-in materials into the dewatering well pipes sequentially, step 5, enabling a cover plate and the waterproof casing pipe to be connected and fixed and enabling a small amount of water to flow out independently from the shock tube, step 6, starting a mud jack pump and compressing curing agents into the dewatering well pipe, and step 7, cutting off the portions, exposed out of the surface of the base plate, of the drainage shock tube, and then using high-intensity concrete to block portions around the well pipe. Thus, blocking of the dewatering well is finished. The decompression type blocking method is wide in application range, high in construction efficiency, convenient to operate, good in water-stop effect and small in later influence.