The mechanism of groundwater flow in the excavation pit with suspended waterproof curtain is very complex. To explore the flow characteristics of groundwater caused by the implementation of the waterproof curtain and pumping well, a novel model is established based on the non-steady groundwater flow in a confined aquifer below a circular foundation pit. By applying Laplace and finite Fourier cosine transforms to the seepage model, the solution of water head drawdown in the Laplace domain is derived. Eventually, the time-domain non-steady groundwater flow drawdown in the confined aquifer subjected to excavation dewatering with suspended waterproof curtain is obtained using the Stehfest method. After the verification of the calculation method and the numerical inverse transformation, the calculation method is further verified in the application to a practical project. Parametric study is also carried out to assess how the flow characteristics of groundwater are influenced by the penetrating depth of the curtain. Results show that the implementation of the curtain has a positive effect on the groundwater control inside and outside the excavation pit. The proposed calculation method provides a new approach for the rational design of the decompression and dewatering of confined aquifer below the circular excavation pit with suspended waterproof curtain.