In this study, a numerical technique was developed to study the effect of processing parameters on instability of the steel during five passes hot bar rolling process. For this a processing map developed based on the plastic work approach was used with finite element analyses to judge occurrence of instability during the process. The effect of roll geometry and processing temperature on hot rolled bars was examined with the help of a parametric study by employing the numerical technique developed. Based on this parametric study, the improved roll pass design and initial processing temperature were determined, respectively, for reducing flow instability during the process. The laboratory rolling mill was used to validate the numerical results. It was found that with the increase of the initial temperature in the process the less flow instability was observed compared to the change of the roll geometry introduced at each pass under the present investigation condition. It was found that the current numerical technique implemented will be useful in identifying the important parameters governing the formation of surface cracks in the multi-stage hot bar rolling process.