In the study of the seismic behavior of concrete cracks in drained slopes on reservoir dams, neither the degradation yield effect of shear strength parameters of rock and soil nor the aging of concrete cracks are considered. This compromises the accuracy of the results of seismic evaluation. Therefore, a method of analysis of the seismic performance of drained slopes on reservoir dams, incorporating concrete cracks, was proposed in this paper. The cracking and failure process of slope concrete under a strong earthquake was simulated, and a judgment of the concrete material yield of the gate pier, according to D-P yield criteria, was made. The thin-layer integral element and separated crack element were used to simulate the concrete crack. After loading the seismic wave, the response and failure characteristics of the concrete cracks under a strong earthquake were obtained. Results showed that the method presented in this paper was highly accurate in studying the displacement change in a dam body; the crack propagation range of concrete obtained was also accurate, indicating the utility of the proposed method.