The hot compression experiment of as-cast ER8 wheel steel under deformation temperature of 900-1250 ℃ and strain rate of 0.001-1 s-1 was conducted by Gleeble-1500D thermal simulation testing machine, and the true stress-true strain curve was obtained. The results show that the true stress-true strain curve conforms to the dynamic recrystallization softening mechanism. At the initial stage of deformation, the hardening of material occurs, and the true stress increases rapidly. However, as the deformation continues, the dynamic recovery of material occurs, and the work hardening rate slows down. Furthermore, in the material deformation process, the distortion strain storage energy of metarial increases, the dynamic recrystallization is activated, the true stress decreases rapidly, and the post-hardening and softening reach dynamic balance. Finally, the influences of deformation temperature and strain rate on the true stress of material at high temperature were analyzed. The true stress decreases with the increasing of deformation temperature and the decreasing of strain rate. By summarizing the experimental data, the hot deformation activation energy of as-cast ER8 wheel steel is 258.4 kJ·mol-1, and the Arrhenius hyperbolic sine constitutive equation was established. In addition, the work hardening rate was solved by the graphing method to find the peak strain and critical strain, and the dynamic recrystallization volume fraction model was established, which accurately predicted the high-temperature softening behavior of this material and provided the theoretical basis for finite element numerical simulation.