Abstract: By use of the elastic plastic finite element method and the method of unequal proportional reduction material strength parameters, the gradual failure process and mechanism, and ultimate bearing capacity of non overflow and overflow segment of Longtan RCC dam at the first and last stages are analyzed, considering the seepage of the dam body and foundation, influences of construction stages, temperature effects and strain softening of the materials. Calculation results show that Longtan RCC dam is safe.