The invention discloses a purifying method of a high-purity silica gel, belonging to the technical field of chemical-mechanical polishing. The purifying method is suitable for purifying silica sol in the chemical-mechanical polishing of a super-large-scale integrated circuit. The purifying method comprises the following steps: uniformly mixing regenerated strong acid cation exchange resin with strong base type anion exchange resin; adding silica sol to be purified in a container filled with strong acid and strong base mixed resin and controlling the temperature, stirring to enable the silica sol to be purified and the strong acid and strong base mixed resin to be mixed uniformly and realizing dynamic purification; and adding a composite chelating agent and a flocculating agent in the dynamic purifying process of the silica sol and controlling the pH value to 1-5 to obtain the purified silica sol. The content of metal ions in the purified silica sol is reduced to ppb level; and the obtained high-purity silica sol can meet the requirement of a substrate or a chip polishing solution for new generation of line width on the purity of the silica sol.