When calculating compressive resistance reliability of gravity dam using the elasticity stochastic finite element method, as a result of stress singularity of dam toe, elements near the dam toe has been encrypted to different mesh size, find a point along the foundation plane that its compressive resistance reliability index is not sensitive to mesh and it is nearest to the dam toe, select the compressive resistance reliability index of the point as the compressive resistance reliability index of gravity dam. Take Longtan RCC gravity dam as an example and give the analysis results.