A loop reactor model in the continuous process for the oligomer formation from terephthalic acid and ethylene glycol was proposed and verified by commercial plant data. The effect of various design and operating parameters, e.g., recycle ratio, residence time ratio of heat exchange to main reactor, feed mole ratio, and feed flow rate, reaction temperature on the degree of esterification, degree of polymerization, DEG concentration, and condensate flow rate was investigated. It was investigated that in case of large residence time ratio of reactor to total loop reactor system and low reflux ratio, both the degree of esterification and degree of polymerization were enhanced whereas the concentration of DEG decreased. Both residence time ratio and reflux ratio should be considered together to maximize the degree of esterification and polymerization. In case the feed temperature of reaction mixture to heat exchange was decreasing, both the degree of esterification reaction and degree of polymerization were slightly affected whereas the concentration of DEG decreased greatly. The reactor performance was enhanced as the feed flow rate decreased. DEG concentration increased with reaction temperature whereas the degree of esterification had maximum point at some reaction temperature. It was expected that the loop reactor model can be applied to the reactor design and process development of real plant since the model was developed based on the real plant data.