Abstract: Leading-edge erosion of rotor blades can induce fan performance degradation and consequently deteriorate the overall performance of an aero-engine.To investigate the impact of leading-edge morphology degradation caused by erosion on fan airfoil performance, a fan rotor of a high-bypass-ratio turbofan engine was selected as the research object. Based on the leading-edge data of the fan rotor blades provided by Xiamen Airlines, a realistic leading-edge morphology conforming to the evolution law of erosion was reconstructed. Using the large eddy simulation (LES) method, the aerodynamic parameters and flow field details at different erosion stages were analyzed. The results indicated that erosion of the leading-edge significantly increased the suction peak intensity and the adverse pressure gradient at the leading edge, which not only led to the formation of a leading-edge separation bubble but also caused premature transition of the boundary layer. At an angle of attack of 0°, the original blade with a circular leading edge was not in an optimal state. Certain leading-edge morphologies at the initial erosion stage could slightly reduce the total pressure loss, whereas the nearly blunt leading edge at the advanced erosion stage significantly increased the total pressure loss. At high-angle-of-attack conditions, the variation in total pressure loss is primarily dominated by the reduction in chord length. At 0° angle of attack, the dominate unsteady fluctuation frequency remained essentially unchanged between the eroded leading-edge blades and the original blade, with the main difference lying in the fluctuation amplitude. Moreover, the amplitude of the wake meandering is consistent with that of the dominant frequency. Finally, the proper orthogonal decomposition (POD) analysis was employed to analyze the energy scales and spatiotemporal characteristics of the dominate unsteady behaviors. The results showed a positive correlation between the complexity of the flow field structure and the complexity of the leading-edge morphology. The wake oscillation dominated the unsteady structures of the flow field, and erosion-induced leading edges caused premature transition on the pressure side, subsequently affecting wake oscillations. his study focuses on the unsteady flow mechanisms at different erosion stages of subsonic airfoils, providing theoretical insights and reference evidence for the mechanistic understanding of the effects of leading-edge erosion on fan rotor blades.