The coke drum is the main reactor of the delayed coking process, in which the deep-severity thermal reaction of heavy oil takes place. To simulate the product distribution in this reactor, a kinetic model for the deep-severity thermal reaction was developed on the basis of the experimental data of a vacuum residuum in a microbatch reactor at 430-490 degrees C. The model predicted results agree well with the experimental values. The ratio of the cracking gas/light distillate rate constant increases with the reaction temperature. Both the primary condensation/cracking rate constant and the secondary condensation/cracking rate constant increase with the reaction temperature. It means that the lower reaction temperature is advantageous to increase the distillate yield at the same reaction severity. Furthermore, a practical transformation method was presented to improve the suitability of this model. The comparison results indicated that this transformation method is available for the kinetic model in this research. Moreover, it can also be used for other lumping models similarly.