Abstract: The hot compression tests were carried out on non-quenched and tempered steel 38MnVTi by using Gleeble-1500D thermal simulation system,and the thermal deformation behavior of the tested steel at temperature of 950-1 200℃and strain rates of 0.01-10 s-1 was studied.Based on Parasd criterion and Murty criterion,the processing maps of dynamic material model(DMM) were built.The instability regions of flow behavior with strain of 0.8 could be recognized by the maps and the differences of the maps were also analyzed.The result show that the instability regions in the two maps were almost equal in area,and the change of numerical feature for the power dissipation coefficient also was similar,but the positions of instability regions were different.The low power dissipation coefficient could identify the instability for hot deformation and the deformation with large strain and high strain rate should be avoided for the tested steel.The best hot deformation progress parameters were the temperature range of 1 050-1 200℃ and strain rates of 0.04-1 s-1.