The crystallization of polymer films in a temperature gradient was simulated. The curvature of lamella growth directions observed experimentally was taken into account. The computer simulation permitted the visualization of the evolution of the spherulitic pattern and also the calculation of the conversion of the melt into spherulites. The mathematical model was also elaborated and allowed the prediction of the kinetics of conversion during the crystallization of polymers in the temperature gradient. A good agreement between the computer simulation results, the mathematical model predictions, and the experimental data for isotactic polypropylene crystallized in a temperature gradient was obtained.