Abstract: To study the warm deformation process of medium carbon steel, the compression experiment was conducted using Gleeble-3500 thermal/mechanical simulator system under the conditions of temperature from 500 to 700 ℃ and the strain rate from 0.001 to 10 s^-1. The experimental results indicate that the deformation process begins from ferrite first, and then the pearlite part, which makes the brokenness of lamellar cementite. Ferrite grain could be refined till 1～2 μm. Slice layer destruction give rise to the peak value of flow stress. Results also show that the flow stress curve of warm deformation is significantly different from that of hot deformation. This research could give some meaningful references to analyze warm plastic forming process and improve the manufacturing technology.