PLA/PBAT/nano-SiO2 composites were prepared through melt blending by using PLA as the substrate, poly (butyleneadipate-co-terephthalate) (PBAT) as the toughening agent and nano-SiO2 as the reinforcing agent. The effects of different mass fractions of nano-SiO2 on the mechanical property, thermal property and rheological property of the composites were studied. The results showed that the bending strength and tensile strength of the composites increased first and then decreased with the increase of nano-SiO2 mass fraction. When the mass fraction of nano-SiO2 was 2%, the improvement in the mechanical properties of the composites was significant, with the bending strength and tensile strength increased by 17.17% and 14.67% respectively. With the increase of nano-SiO2 mass fraction, the initial decomposition temperature and half-life temperature of the composites increased by 5~8 ℃ and 8~10 ℃, the glass transition temperature and melting temperature increased by 1~3 ℃ and 3~6 ℃ respectively, indicating enhancement of the thermal stability of the composites. Rheological properties test showed that the shear viscosites of the composites with nano-SiO2 were higher than that of the composites without nano-SiO2 at three different temperatures. The difference of the shear viscosity between the two composites decreased with the increase in temperature, indicating the weakening of the intermolecular force. The composite materials could be processed at 155~165 ℃. The composite melts were pseudo plastic fluid. With the increase in temperature, the flow index increased gradually and the consistency coefficient decreased gradually, indicating that the pseudoplasticity of the composite decreased and the flowability improved.