Land subsidence caused by decompression of confined water is comprised of deformations of aquifer, aquitard and phreatic stratum. When the decompression features short duration so that consolidation deformation of aquitard is little, the aquitard is supposed to be watertight. Theory for elastic layered system is adopted to calculate layered soil deformation caused by dewatering of single well and the third type of foundation pit dewatering that the waterproof curtain inserts into the confined aquifer. The calculated results are compared with numerical simulation and in-suit tests results. The analytical results show that elastic modulus of the overlying soil has little influence on ground surface displacement; yet thickness of overlaying soil layer shall be taken into consideration. The settlement of soils overlying confined aquifer increases up to down nearby the pumping well. Over a certain distance, the settlement does not change with depth. The drawdown outside the foundation pit can be estimated according to the demand for drawdown inside the foundation pit.