Abstract: With commercially available silica sol as the crystal seed and sodium silicate as raw material，a high-purity silica sol with 20~24 nm in particle size and with 40% in mass fraction was prepared by ion exchange and complexing purification method.The main influencing factors，such as seed concentration，reaction pH，and impurity removal，in the preparation pro- cess of silica sol were analyzed.The prepared product was analyzed by transmission electron microscope（TEM），nano zetasizer， and BET.The experimental results proved the feasibility of the process，and their application effect in hydrofining catalysts was also tested.

Key words: sodium silicate, silica sol, seed concentration, reaction pH