This paper firstly stated the fabrication of silica particles via Sol-Gel method and their modification by Silane coupling agent ${gamma}$-MPS (3-Methacryloxypropyltrimethoxysilane). Pure PSt (Polystyrene) and silica/PSt microspheres were prepared via miniemulsion polymerization. We added these two microspheres to SX-5 size respectively to form the nano-modified sizes. These nano-particles were characterized by means of FTIR (Fourier Transmission Infrared Spectroscopy), DLS (Dynamic Light Scattering) and TEM (Transmission Electron Microscope). Then the properties of sizes (SX-5, nano-modified SX-5, PVA (Polyvinyl Alcohol) 1799), size films, sized yarns, and removability of sizes were characterized. Experimental results show that silica/PSt modified SX-5 had the best properties of sizes, and the best properties presented in size films and sized yarns. This result can be suggested that small size effect, high fluidity, high surface energy and tough surface morphology of silica/PSt microspheres, playing a role as cross-linker and reinforcement, will enhance the mechanical properties of SX-5 and increase the interfacial adhesion force between sizes and yarns.