Abstract: The stress-strain curves of 40CrNiMo steel at the strain rates of 0.1-50 s^-1 and deformation temperatures of 800-1 100℃ were obtained by single pass hot compression experiment on the Gleeble-3500 thermo-simulation machine. The microstructure after deformation was observed and the hot deformation characteristics of 40CrNiMo steel were analyzed. The deformation resistance model of the steel was established and verified by experiments. The results show that the relatively high deformation temperature or relatively small strain rate were favorable for the complete dynamic recrystallization of 40CrNiMo steel. When the deformation temperature was 800℃, the amount of dynamic recrystallization grains increased with the increase of the strain rate. When the strain rate was 10 s^-1, the amount of dynamic recrystallization grains increased when the deformation temperature increased from 800℃ to 900℃; the complete dynamic recrystallization of 40CrNiMo steel occured at the defermation temperature of 1 000℃; the dynamic recrystallization grains grew up at the deformation temperature of 1 100℃. The calculated dynamic recrystallization activation energy of 40CrNiMo steel was 322.53 kJ·mol^-1. The average relative error between deformation resistance calculated by ZHOU Jihua-GUAN Kezhi model and experimental values was 4.82%, indicating a relatively high accuracy.