Under the influence of construction, age, environment and the repeated static and dynamic loads of the dam in service period, the dam body and the layer have different degrees of deterioration damage, and the mechanical parameters of the dam rolling layer and the surface layer show gradual change. According to the gradient characteristics of compacted layer mechanical parameters, the corresponding equivalent algorithm of physical parameters is proposed, and the mathematical transformation relation between coupling parameters is given. The interaction mechanism of stress and seepage is analyzed, then the coupling analysis model of seepage field and stress of the RCC dam considering the gradation of parameters in the layer is established, and the corresponding finite element analysis program is compiled. The engineering case study shows that the coupling effect leads to the change of the dam seepage field, the stress increases of the dam body, and the significant stress concentration at the dam heel. The unfavorable factors under the coupling of seepage field and stress field can provide a scientific basis for the design, construction and safe operation of the dam.