Abstract: Isothermal compression experiments were conducted to investigate the hot deformation behavior and microstructural evolution of 20Cr2Ni4A steel under deformation temperatures of 900-1100 ℃, strain rates of 0.01-10 s^-1, and true strains of 0.8. The true stress-strain curves indicate an increase in flow stress with increasing strain rate and decreasing deformation temperature. Significant peaks are observed in the flow curves at deformation temperatures of 950-1100 ℃ and strain rates of 0.01-0.10 s^-1, demonstrating pronounced softening effects. The constitutive equation of the 20Cr2Ni4A steel was established based on the peak stress, and the deformation activation energy was calculated to be 489.24 kJ/mol. Utilizing a dynamic materials model, a processing map was constructed at a true strain of 0.8, revealing that high strain rates and low deformation temperatures were more likely to induce flow instability. Microstructural analysis shows that at low temperatures and high strain rates, the predominant deformation mechanism involves elongated deformed grains. Complete dynamic recrystallization occurs at deformation temperatures ranging from 975 to 1030 ℃ and strain rates ranging from 0.07 to 0.20 s^-1,resulting in a fine and homogeneous microstructure that effectively mitigates the unevenness in the initial grain size.