Due to the complex interaction of the motor mechanical and thermal aspect, this paper demonstrate how the operating thermal field affect the dynamics performance of HSPM rotors. The actual assembly rotor-shaft-turbine model is proposed to calculate the critical speed by both transfer matrix method and finite-element method. The influences of the modulus of elasticity and the thermal stress, produced by temperature rising, on critical speed are analysis in detail. The thermal-structure-dynamic coupling computation is conducted by FE modal analysis considering the rated operation situation, the real contact behavior and the cooling fluid flow condition. It provides references for HSPMSM design to improve accurate prediction critical speed.