The induction period is a significant concept for design and operation of the delayed coking process. To simplify the prediction of the induction period and make it applicable to operational analysis and real-time control of the thermal cracking process, a practical model for the induction period of heavy oil during thermal reaction, which is suitable for the non isothermal reaction in the industrial conditions, was presented. The development of this model was based on the experimental data of five heavy oils. The model parameters were correlated with microcarbon residue (MCR) of heavy oil to improve the model universality. Furthermore, the validity of correlation between MCR and cracking kinetic parameters was proven. The model-predicted cracking conversion agrees well with the experimental values. The induction period model was employed to predict the induction period of two feedstocks reported in the literature. Results indicated that the induction period model is available for the thermal reaction of these heavy oils.