Abstract: The coupled effects of temperature and strain rate are important factors influencing the dynamic service performance of high-entropy alloys. In this study, CoCrFeNi high-entropy alloy was selected as the research object. Dynamic compression tests were conducted under different temperature and strain-rate conditions using a split Hopkinson pressure bar, and the dynamic mechanical response and deformation mechanisms were systematically analyzed in combination with microstructural characterization of strain-frozen specimens. The results show that the CoCrFeNi high-entropy alloy exhibits strain-rate strengthening effect during dynamic compression and maintains a favorable strength-ductility balance under high-temperature dynamic loading. Its strain-rate sensitivity is closely related to both strain level and temperature. Microstructural analysis indicates that plastic deformation of the high-entropy alloy is dominated by dislocation slip, while slip bands, deformation twins, and dynamic recrystallization act synergistically at different deformation stages to regulate the plastic deformation process. The formation of slip bands and deformation twins contributes to accommodating intragranular deformation, dispersing local strain, and enhancing strain-hardening capacity. With increasing deformation, dislocations accumulate and interact at and near twin boundaries, promoting the nucleation of recrystallized grains. Dynamic recrystallization alleviates local strain concentration through dislocation annihilation, release of stored strain energy, and microstructural refinement, thereby helping to maintain the strength and plasticity of the high-entropy alloy during dynamic deformation. In addition, under the same strain condition, increasing temperature has a certain inhibitory effect on the formation of deformation twins. This study provides a reference for microstructural regulation and performance optimization of CoCrFeNi high-entropy alloys under dynamically coupled thermo-mechanical service conditions.