An efficient processing modifier silica-g-poly (lactic acid)/poly(propylene carbonate) (SiO2-g-PLA/PPC) was synthesized by grafting reaction and poly(lactic acid)/poly(propylene carbonate) (PLA/PPC) nanocomposites were prepared using a Haake torque rheometer. Fourier transforms infrared (FTIR) spectrometry, H-1 nuclear magnetic resonance (H-1 NMR), thermogravimetric analysis (TGA), and theological results showed together that the PLA and PPC Molecular chains were successfully grafted on the surface of nanosilica (nano-SiO2). The scanning electron microscopy (SEM) photographs showed that SiO2-g-PLA/PPC could effectively improve the interface adhesion of PLA/PPC blends, so that the compatibility of the two improved. Moreover, SiO2-g-PLA/PPC could effectively toughen PLA/PPC blends, accelerate crystallization and increase the relaxation time of PLA/PPC blends which leads to an improvement of processing performance effectively. All of the above improvements of PLA/PPC nanocomposites were attributed to the strong entanglements between polymer chains grafted on the nano-SiO2 and the polymer matrix.