<p>Machined surface localization is one of the most significant dynamic behaviors in the high-speed machining process, inevitably leading to the thermo-plastic damage initiation and development in the machined surface layer. In this paper, the thermo-plastic damage characteristics during machined surface localization in high-speed machining of rail steel were further investigated based on the proposed damage coupled constitutive theory of machined surface layer. Considering the dynamic recovery and recrystallization mechanisms in the pre-peak stage and the dynamic damage evolution mechanism in the post-peak stage, the damage coupled thermo-visco-plastic constitutive model was constructed and verified through the high-rate impacting experiments (strain rate: 10³~10⁴ s^− 1) and the high-speed machining experiments (cutting speed: ~1200&#xa0;m/min, uncut thickness: 0.2&#xa0;mm/r, rake angle: -10°). The related influence laws of the physical properties, the constitutive parameters, and the dynamic variables on the machined surface layer damage were quantitatively analyzed and thoroughly discussed. The experimental and analytical results showed that the rail steel was a rate-hyposensitive material relative to its thermal sensitivity under high-rate loading conditions. The rail steel with low density, good thermal conduction and high mass heat capacity was prone to energy convergence under low temperature rise and large shear stress, resulting in fast surface damage accumulation. The propagating speed and time of thermo-plastic shear wave directly influenced the surface damage development.</p>