Abstract: Hot compression deformation of steel 34CrMo4H with strain rate 0.1 ~ 10 s^-1 at 800 ~ 1200 ℃ has been tested and studied by using Gleeble-3800 thermo-mechanical simulator to analyze in hot deformation of this steel. The relationships between flow stress and strain rate, as well as flow stress and deformation temperature were studied. Results show that the flow stress increases with the increase of strain rates and decreases with the increase of temperature, and as the strain rate is 0. 1 s^-1, the feature of dynamic recrystallization occurs obviously on flow stress curves of steel. The hot deform activation energy of steel 34CrMo4H is 395.45 kJ/mol.