In order to improve the mechanical properties of PPC, a hyperbranched polymer with a large number of active epoxy groups at the end (epoxy-terminated hyperbranched polyester, EHBP) was synthesized and characterized by FTIR, NMR and GPC. Then, PPC/EHBP blends were prepared through melt-mixing. The effect of EHBP on the mechanical properties, thermal properties, viscosity and gas permeability of the PPC/EHBP blends is studied in detail based on the expected micro-crosslinking theory between EHBP and PPC. The results indicate that when the content of EHBP is 0.5 wt%, the tensile strength increased by 73.8%; elongation at break increased by 131.7%; the impact strength increased by 88.4%. The glass transition temperature increased from 40.71 to 44.44 degrees C upon addition of EHBP. Also, the addition of EHBP is beneficial to the improvement of the gas barrier property of PPC. The modification mechanism is discussed. It indicates that upon addition of EHBP, both physical hydrogen bonding and chemical bonding occurred, based on gel content calculation, which is in line with expectations. When the content of EHBP is 0.5 wt%, the degree of chemical micro-crosslinking is about 9.2%.