Dispersion of nano-particles plays a key role in preparing high-performance nano-composites. Steric hindrance stability mechanisms can be applied to improve the dispersibility and stability of nano-particles. The steric hindrance layer can be established when graft polymerization of PBT prepolymer is performed onto the surface of nano-particles. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectrosopy (XPS) characterization revealed the chemical linkage between nano-silica and the grafted prepolymer. Based on XPS and thermal gravimetric analysis (TGA), it is conjectured that the grafted PBT prepolymer was mainly distributed on the surfaces of nano-silica. From transmission electron microscopy (TEM) images the polymer coverage can be observed. System vacuum played an important role in determining the graft amount and the length of the grafted chains. The relationship between vacuum and chain length was investigated by calculating M, and TGA. The lower the vacuum, the more the weight loss, and thus the longer the grafted chains. Sedimentation experiments and atomic force microscope (AFM) characterization showed that the grafted nano-silica prepared under the vacuum of 3.9 kPa had the best dispersibility and could disperse homogeneously in tetrachloroethane. Under these conditions, the length of the grafted molecule chains was approximately, 16 units.