A comprehensive model for solid-state polymerization of poly(ethylene terephthalate) was developed from analyzing the similarities and the differences between solid-state and melt polymerization. Considering the end groups diffusion limitation and the modification of concentrations of end groups and byproducts in the amorphous phase, a system of mass transfer and balance equations suitable for the solid-state polymerization of PET were obtained, based on simplifying the reaction kinetics of melt polymerization of PET. The degradation and other side reactions neglected in the earlier models for the solid-state polymerization of PET were included in the model. This simulation gave a quantitative prediction in the effect of temperature, particle size, starting molecular weight, and ratio of end groups on the degree of polymerization of products during the solid-state polymerization of poly(ethylene terephthalate). These simulation results were in agreement with experiments.