A dynamic model combining molecular kinetic theory and classical nucleation theory was used to simulate the heterogeneous vapor-to-crystal phase transition in a closed vacuum chamber at low substrate temperature, The governing equations for the moles of molecules adsorbed to the substrate, the pressure in the chamber, and the number and mass of the crystals formed were simultaneously integrated. The model showed that the heterogeneous phase transition changed from one controlled by crystal growth to one controlled by heterogeneous nucleation as the condensation coefficient decreased, On the basis of the observation and the assumption for the adherence between the crystals and the substrate surface to be incomplete, the substrate temperature and the crystal surface temperature, respectively, were raised by 0.4K and by 1K at the onset of nucleation in the model computation, The changes in vapor pressure with elapsed time in the computed results agreed reasonably well with the experimental ones.