A mathematical model of the industrial continuous process polymerization of epsilon-caprolactam into polyamide 6 (nylon 6) was developed. The model considers a kinetic solution of all reactions taking place in the process, namely ring opening of caprolactam, polycondensation, polyaddition, ring opening of cyclic dimers, polyaddition of cyclic dimers, and in this case, the reaction with acetic acid. The analysis is based on the assumption of plug flow in all reactor zones (model M1) and ideal mixing in the top zone and plug flow in the lower reactor zones (model M2). The model also considers the temperature profile during polymerization and the variation of residence times in the reactor due to the heating bodies placed inside the reactor. The mathematical model was tested on two industrial continuous flow reactors for various flow rates and different temperature profiles. The results of numerical calculations were in all cases in very good agreement with the experimental data.