A combination of hexamethylene diisocyanate (HMDI) and hyperbranched epoxy resin (HBPs) was used as a composite chain extender and reacted with PET through reactive extrusion to achieve hyperbranched chain extension of PET, obtaining PET-HMDI/HBPs. The properties of PET-HMDI/HBPs were studied using differential scanning calorimetry, rotational rheometers, melt flow index testing, and a universal testing machine. The experimental results show that when the HMDI/HBPs addition was 3/2, the melt flow index of PET-HMDI/HBPs was 60.12 g·10min?1, the intrinsic viscosity was 1.45 dL·g?1, the viscosity-average molecular weight was 48,279 g·mol?1, the tensile strength was 82.10 MPa, and the crystallinity reaches as high as 29.10%. The storage modulus, loss modulus, and complex viscosity of HMDI/HBPs/PET were significantly improved, broadening the scope of recycling and processing applications for PET materials.