Abstract: Leakage occurred in the deep foundation pit of an interval air shaft during the earth excavation. The depth of the leakages is 32m and a great deal of water busted immediately. Firstly, the Metro Jet System (MJS) and WSS methods can not achieve the reinforcement effect. Finally, the method of grouting reinforcement is adopted after the surrounding of underwater low-grade impermeable plain concrete wall and the original end reinforced plain concrete wall is formed on the East and west sides of the foundation pit. After the reinforcement treatment with this method, the velocity and flow value of the measuring hole outside the plain concrete measured by the sonar method are obviously smaller than those of the measuring hole outside the reinforced concrete diaphragm wall (inside the plain concrete wall), and the average velocity values of the 21 measuring holes outside the plain concrete wall are less than 6.0 × 10-6cm / s, it can be seen that the plain concrete wall outside the foundation pit has the expected effect of strengthening the water stop; The tracer test and micro water test show that the permeability coefficient of the soil layer after reinforcement is in the order of 10-4cm / s, the reinforcement effect is obvious, and the surrounding precipitation effect is obviously improved. After reinforcement, no water and sand gushing occurred in the process of re excavation, and the construction of air shaft floor structure was successfully completed, which proved that the reinforcement method was effective.