The invention discloses a novel surface sizing system--chitosan/silica sol double sizing system: it combines the degraded chitosan with silica sol to form a stable complex system of organic matter and inorganic matter. The mass ratio of sugar to silica sol is 2: 3 - 1: 9. Water-soluble chitosan is prepared by hydrogen peroxide oxidation degradation method. Silica sol is synthesized by the dissolving method of monatomic silicon. The new paper making agent formed by the compounding is applied to the surface sizing of cultural paper. it can obviously promote the water resistance on the paper surface, surface strength, the degree of internal bonding, galling speed and other properties, improving printing performance and meanwhile reducing the cost of sizing.