A physical metallurgy principle based model to predict flow stress, recovery, recrystallization and precipitation of Nb-containing micro-alloyed steels during hot rolling is developed. Precipitation kinetics is simulated by the model during hot rolling. The driving force and the equilibrium concentrations are calculated by Thermo-Calc software. The volume fraction of precipitation particles and the particle size of Nb-containing micro-alloyed steels during hot rolling are calculated with considering the effect of recovery and recrystallization on precipitation. The model is verified by the experimental results, and the volume fraction of precipitation particles and the particle sizes are predicted in different hot rolling processes.