Abstract: The thermo-elastic characteristics of friction pairs directly affect the working performance and reliability of hydro-viscous drive.In order to study the effect of temperature changes and external constraints on the thermo-elastic characteristics of friction pair during the soft start-up process, the transient heat conduction and thermo-elastic axisymmetric model were established.Comprehensively considering the thermal stress and mechanical stress, the indirect coupling finite element numerical analysis method was used to predict the distributions of temperature, stress, and displacement field of the steel disc.The mechanism of thermal failure of steel disc was revealed.The results show the important effect of thermal load on the stress field and thermal failure of steel disc.When the stress exceeds the yield strength of the material, the saucer-shaped warping deformation of steel disc may occur.The circumferential stress is the most important stress component and can be used as the basis for assessing the thermal failure of steel disc.The research results provide a theoretical reference for designing the friction pairs and improving their working performance.