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In a high-speed permanent-magnet generator (HSPMG), an alloy sleeve is often used to prevent damage to rotor magnets caused by the large rotational centrifugal forces. However, eddy-current losses appearing in the sleeve increase the generator working temperature, which may reduce the generator performance and even cause thermal demagnetization of the magnets. Thus, a sleeve scheme designed with low eddy current losses is necessary, and a rotor structure with copper plating is presented in this paper. The two-dimensional mathematical model of a 117 kW, 60 000 rpm HSPMG is established, and the electromagnetic field in the generator is calculated using the finite element method. The results show the effectiveness of the copper plating in reducing the eddy current losses in the rotor, and the influences of the sleeve thickness and the copper layer thickness on rotor eddy current losses are analyzed. Using the fluid-thermal coupling method, the temperature distribution of the generator with different copper layer thicknesses is comparatively analyzed based on the theories of fluid mechanics and heat transfer. The relationship between the temperature and the copper layer thickness is obtained, and finally the temperature of the permanent magnets, which is the part most seriously affected by the temperature, is given with different copper layer thicknesses. The obtained conclusions may provide useful reference for the design and research of HSPMG.