The use of the jet-grouted bottom sealing barrier reinforcement at the bottom of the pit during excavation is an efficient measure to reduce the impact of groundwater seepage on the pit. Once a local defect appears in the barrier, groundwater will pour into the pit, which will obstruct construction and even induce inrush accidents, threatening construction safety. Regarding to this problem, a simplified numerical model was established for the calculation of seepage inflow at the bottom of a rectangular pit with a defected sealing barrier, by which the formula for calculating the seepage inflow was derived. Then, GeoStudio was adopted to simulate the seepage field of the barrier with a local defect, and the results were compared with those of the previous derived formula, so as to discuss the applicable conditions of the formula. The results show that the defect impermeability coefficient δ(the ratio of the permeability coefficient of the undisturbed soil to that of the defect in the barrier) is the main factor affecting the accuracy of the formula, and the relative error between the calculated and simulated values tends to decrease with the increase of δ, when δ≥20, the calculated value is consistent with the simulated value, the difference in waterhead at the bottom of the seepage barrier has a small effect on the amount of seepage; when δ＜20, the relative error between the calculated and simulated values is large, a half-theoretical, half-empirical equation obtained by correcting the theoretical equation empirically can better reduce the error in the calculation of seepage volume caused by the difference in waterhead at the bottom of the sealing barrier. The results of the study have a certain referential value for the calculation of the inflow at the bottom of the pit and the analysis of barrier quality.