In view of the analysis of rotor strength of surface mounted permanent magnet motor in high speed and high temperature condition, a rotor model considering magnetic steel with block structure was proposed. Based on the theory of thick walled cylinder, the analytical solution was derived. The tangential and radial stresses of carbon fiber sleeve and magnetic steel were respectively calculated. Based on finite element method, the rotor strength under various working conditions was analyzed. The stress on the rotor would increase under both high speed and high temperature conditions. Compared with the analytical analysis results, it showed that the finite element method and the analytical method could accurately calculate the stress of the carbon fiber sleeve, while the magnetic steel stress would be affected by the edge effect, so that the analytical analysis could not perform accurate calculations. The interference amount between the sheath and the magnetic steel was analyzed by the finite element method, based on which the rotor structure was optimized and the optimal range of the interference amount was given.