Abstract: In the paper, the FEM is used to obtain the dam stress, and the limit state equation of tensile reliability for gravity dams is established with the possible tensile stress distribution width being set as action effect and the allowable tensile stress distribution width being set as resistance. This limit state is implicit. The linear response surface method is applied and the orthogonal test design method is used to reduce the number of finite element analysis. The Longtan RCC gravity dam is taken as an example and the analysis results are also given.