The polycondensation of poly(ethylene terephthalate) (PET) in both melt and solid states was conducted with high pressure CO2 and ambient pressure N-2 sweeping to remove the volatile byproducts, revealing that only the solid state polycondensation (SSP) of PET could be facilitated by high pressure CO2 due to the substantial increase of free volume. With the comparison of SSP processes of PET in dynamic and static CO2 supplying modes, a periodical supercritical CO2 renewing strategy for SSP of PET was proposed. The SSP process was promoted significantly, and only 6 h were required from the degree of polymerization of 100 to 150, while it takes nearly 20 hours in the industrial SSP process of PET. The effects of CO2 renewing period, CO2 pressure, reaction temperature, and initial molecular weight on the newly proposed SSP strategy were investigated, and a semiempirical kinetic model was applied to fit the experimental data well.