Abstract: Based on the failure mechanism of bearing resistance water foundation pit base plate, a method for calculation of critical pit base plate thickness of foundation is proposed. It is conceptually simple and easy to be implemented. It considers the influence of all foundation pit plane dimensions except the depth of foundation pit excavation. Therefore, it can reflect truly the stability of sudden gush resistance of foundation pit. Results show that among the five engineering examples, the results gained by the present method conform with the real conditions to 80%, contrasting with the 20% agreement achieved using the traditional method.