A combination of hexamethylene diisocyanate ( HMDI) and hyperbranched epoxy resin ( HBPs) was used as composite chain extender and reacted with polyethylene terephthalate ( PET) through reactive extrusion to achieve hyperbranched chain extension of PET, obtaining PET-HMDI/ HBPs. The properties of PETHMDI/ HBPs were studied by differential scanning calorimetry, rotational rheometers, melt flow index testing, and universal testing machine. The experimental results show that when the HMDI/ HBPs mass ratio is 3 / 2, the melt flow index of PET-HMDI/ HBPs is 60.12 g / 10 min, the intrinsic viscosity is 1.45 dL / g, the viscosity-average molecular weight is 48279, the tensile strength is 82.10 MPa, and the crystallinity reaches as high as 29.10% . The storage modulus, loss modulus, and complex viscosity of HMDI/ HBPs/ PET are significantly improved, broadening the scope of recycling and processing applications for PET materials.