With industrial-grade sodium silicate as precursor material, HCI as precipitating agent, polyethylene glycol (PEG) as surfactant and silica coupling agent (γ-Trimethoxysilyl-propyl- methacrylate, KH570) as modifier, net and modified nanosilica(nano-SiO2)were prepared by chemical precipitation method and in situ modification respectively under multiple shear force field. The influence of ethanol and water volume ratio, sodium silicate concentration, salt dosage, pH value of the solution , modification methods, surface active agent or other modifier dosages on the appearance of nano-SiO2 were analyzed and the preparation of nano-SiO2 formula was optimized. The resultant materials were characterized by transmission electron microscope (TEM) and laser particle size analyzer. The results showed that the optimized formulation of the nano-SiO2 prepared by chemical precipitation method under multiple shear force field were the ethanol and water volume ratio 1:4, the quality fraction of sodium silicate about 12 %, the quality of PEG, KH570 and sodium chloride respectly 40 %, 5 % ~ 10 % and 30 % of the theoretical required quality and the best pH value about 9.