Abstract: The anti-sliding stability is the most basic requirement for gravity dams. It can be regarded as the abnormal deformation behavior. The traditional ways to determine the early-warning value of dam deformation safety are commonly based on deterministic structure parameters and mathematical models. The uncertainty characteristics of the relevant influencing factors lack consideration. In order to solve the above problem, the theory of uncertainty analysis is applied. In this paper, the response surface method is introduced to fit the functional relation between the water pressure component of gravity dam deformation and the anti-sliding stability reliability index based on the analysis of the correlation between dam deformation, anti-sliding stability reliability index and water depth before the dam. According to the current reliability design specification, an anti-sliding stability reliability index-based approach determining the early-warning value of deformation safety for gravity dam is proposed and verified in the actual engineering case. The rationality of the conclusion is proved by comparing with the result of the typical small probability method. The proposed method can be regarded as useful complements and mutual verification means for the traditional methods.