Transonic fan rotor blades will suffer from morphological decay problems such as leading edge erosion in actual operation, and the flow field structure in the tip zone will change and then induce aerodynamic performance degradation. The effects of leading edge erosion on the tip leakage flow of the fan rotor were investigated from constant numerical computation in this paper. The results show that at the stall point of the eroded blade, its isentropic efficiency, total pressure ratio and mass flow rate decrease by 4.3%, 0.43% and 5.63%, respectively, and the leading-edge erosion also causes a decrease in the stabilized operating margin by 0.69%. For the flow in the tip zone, the leading-edge erosion causes an increase in the entropy increase area and intensity in the flow surface of S1 at the tip zone and the flow surface of S3 in the exit region, and the formation of a low Mach Number flow region in different blade heights; the leakage flow structure under the leading edge erosion undergoes malignant changes, the demarcation point of the main leakage flow and the secondary leakage flow is advanced, carrying more fluid for secondary leakage, and the leakage vortex deflection angle of the eroded blade reaches 30° from 15°, hitting the leading edge of the blade directly and causing flow blockage.