The leakage characteristics of the water stop curtain directly affect the safety of foundation pit engineering. If the leakage location and permeability coefficient can be quantitatively analyzed based on the characteristics of water level changes outside the pit, the risk of groundwater leakage can be controlled throughout the entire lifecycle of the foundation pit engineering. This study establishes a finite element model and employs orthogonal experiments to analyze the sensitivity of water level drawdown to four factors: the insertion ratio of the water stop curtain, the permeability coefficient ratio of the leakage position, the observation hole position (distance to depth ratio), and the leakage position. Furthermore, the influence mechanism of each factor is further analyzed; Based on the characteristic curve of water level drawdown, a calculation method for the permeability coefficient of the leakage location is proposed. The results show that: (1) The sensitivity level is in the order of permeability coefficient ratio>distance to depth ratio>water stop curtain insertion ratio>leakage location; (2) The sensitivity of water level drop to the permeability coefficient ratio and width-to-depth ratio differs between suspended and bottom-type water stop curtains; (3) There is a critical permeability coefficient ratio, and when the permeability coefficient is less than the critical value, as the insertion ratio increases, the leakage flow rate decreases; When the permeability coefficient is greater than the critical value, the leakage water volume increases sharply and increases with the increase of insertion ratio, the change in hydraulic gradient is the reason for this difference; (4) The drawdown difference of water level has an exponential function relationship with the width depth ratio, and a linear relationship with the insertion ratio and the permeability coefficient ratio. The leakage location and permeability coefficient can be obtained by solving the water level drawdown curve together.