In hot forming processes, the evolution of microstructural features such as deformation texture and dislocation substructure and their mechanical properties are affected by thermo-mechanical history. In order to analyze these processes, both the plastic deformation of the workpiece and its microstructural changes should be taken into consideration. In this paper, application of the flow stress prediction model to the simulation of hot forming is presented. The model is implemented in the thermo-viscoplastic finite element simulation for the hot upsetting process, temperature, strain rate and flow stress distributions, therefore the geometry of the workpiece at each time step can be calculated. Validation of the model and typical examples of simulation are presented.