Constitutive analysis for hot working of Aermet100 steel was carried out using experimental stress-strain data from isothermal hot compression tests, in a wide range of temperatures (1073~1473 K), strains (0.05~0.9) and strain rates (0.01~50 s-1). A constitutive equation based on orthogonal experiment has been established considering the independent effects of strain, strain rate and temperature. With consideration of the effects of the deformation temperatures and the stain rates on microstructures and properties of Aermet100 steel, processing maps were established based on the dynamic material model (DMM). And the instability zones of flow behavior could also be recognized by the maps. The hot deformation characteristics of Aermet100 steel in different zones were also analyzed.