Abstract: Fatigue tests are conducted on tapered plain concrete prism specimens subjected to constant-amplitude or variable-amplitude triaxial tension-compression cyclic loading. The low level of the cyclic stress is 0.20ƒ_c and the upper level ranges between 0.20ƒ_t and 0.55ƒ_t. The constant lateral loading is 0.30ƒ_c. The three-stage evolution rule of the maximum and minimum longitudinal strains under constant-amplitude loading and its similarity under variable-amplitude loading are analyzed. The damage evolution law under both loading cases is obtained. Moreover, it is proved that Miner's rule is not applicable. A nonlinear cumulative damage model is established. Based on the model the residual fatigue life is predicted and compared with the experimental results. The better precision and applicability of the model is demonstrated.