The stable and controllable deformation of deep foundation pit in water-rich sandy strata was the basic guarantee of underground engineering construction safety. Aiming at the leakage disaster of deep foundation pit in water-rich sandy strata, this paper takes the leakage incidents of launch shaft pit of subway station as the research background, summarizes and analyzes the development process and accident causes of water and sand leakage disaster through field investigation and survey data review, the characteristics of horizontal displacement of retaining wall, ground settlement behind wall and change of groundwater level outside the pit during partial leakage were systematically studied, and the effect rules of partial leakage on the deformation behavior of foundation pit were revealed by numerical simulation method. The results of research shows that the horizontal displacement of the retaining wall increases significantly due to partial leakage, and the maximum horizontal displacement of retaining wall after leakage is 1.29 to 1.47 times that before leakage. The ground settlement trough of sensitive zone deepens and widens due to partial leakage, and the maximum ground settlement after leakage is 1.16 to 2.67 times of that before leakage. The characteristics of "jump" fluctuation of groundwater level can be used as an important criterion for the precursor of leakage disaster in foundation pit. The combined treatment measures of grouting and high pressure rotating spouting pile can effectively deal with the problem of leakage disaster control of foundation pit in water-rich sandy strata.