This paper proposes an integrated model for the prediction of the pass-by-pass evolution of the austenite grain size of the ribbed steel bar hot rolling. The integrated model consists of a strain model, a temperature model, a microstructure evolution model of austenite grain size and a flow stress model. Hot rod rolling experiments are conducted to examine the proposed analytical models. The integrated model is employed to examine the effects of modifications of the refined austenite grain size of the 500MPa ribbed steel bar. Refinement of ferrite could be realized by refining the austenite grain size at the final pass.