Abstract: Fretting fatigue is a common failure mode in engineering structures. It manifests as the degradation of fatigue strength or even early fracture due to micro-slip at the contact surface under the combined action of normal and cyclic loads. This study addresses the shortcomings of existing single-scale analysis methods and hierarchical multi-scale methods in revealing crack initiation mechanisms and improving life prediction accuracy. It constructs an embedded two-scale model based on continuum damage mechanics and crystal plasticity. By introducing a power-law scale correlation mechanism, the model quantitatively links the accumulated dissipation energy at the mesoscopic grain scale with macroscopic damage. It clarifies the fretting fatigue crack initiation mechanism and establishes a life prediction method from both macroscale and mesoscale. Numerical simulation results show that, at the macroscale, the two-scale model predicts crack initiation life and location with higher accuracy compared to traditional single-scale methods. At the mesoscale, it provides insights into the evolution of microstructures and the preferential activation of slip systems in grains, revealing that material damage exhibits nonlinear accumulation characteristics, and grain boundary regions become energy dissipation hotspots due to orientation differences and morphological heterogeneity. Additionally, the application of the two-scale model to fretting fatigue analysis of friction-type high-strength bolted connections successfully implements a transition from mechanistic investigation to engineering practice. The two-scale analysis method proposed in this study is expected to provide a theoretical framework and numerical analysis tool for assessing the fretting fatigue life of engineering structural components.