NOVELTY - A composite sol is prepared as follows. A silicate, an alcohol solvent, a basic catalyst, and deionized water are aged and pH-adjusted to obtain sol (A). A silicate, an alcohol solvent, an acidic catalyst, and water are preheated to obtain sol (B). The sols are aged, and silane coupling agent is added, hydrolyzed, and aged to obtain sol (D). Sol (D) is filtered, and metal salts are added and aged to obtain sol (E). A film-forming fluxing agent is added, silica solid content is adjusted, and pH is adjusted after aging to obtain the composite sol.    USE - Composite sol is used for antireflection coating films of seal glass used as photovoltaic glass (claimed).    ADVANTAGE - The composite sol can be prepared by an economical method, with efficient and liable control. The composite sol forms films having excellent hardness, adhesiveness, and weather resistance.    DETAILED DESCRIPTION - A composite sol is prepared as follows. A silicate, an alcohol solvent, a basic catalyst, and deionized water are taken in a volume ratio of 1:1-20:0.05-0.5:0-0.5, and stirred and preheated at 15-60 degrees C for 1-2 hours. The pH of obtained mixed solution is adjusted to 7-9. The solution is seal-aged at 15-60 degrees C for 96-240 hours, heat-boiled for 1-12 hours, and pH-adjusted to neutral to obtain sol (A). A silicate, an alcohol solvent, an acidic catalyst, and water are taken in a volume ratio of 1:1-20:0.0005-0.05:0-0.5, pH-adjusted to 5-7, and stirred and preheated at 15-60 degrees C for 1-12 hours to obtain sol (B). Sol (A) and sol (B) are mixed in a molar ratio of 1:0.25-4 based on silica content, stirred, and seal-aged at 15-60 degrees C for 24-96 hours to obtain composite sol (C). A silane coupling agent is added to composite sol (C) and stirred for hydrolysis. The mixture is seal-aged at 15-60 degrees C for 48-120 hours and pH-adjusted to 5-7, to obtain composite sol (D). Sol (D) is filtered, and aluminum and/or titanium alcohol-soluble metal salts are added such that molar ratio of silica content and metal ions is 1:0-0.2. The mixture is seal-aged at 15-60 degrees C for 48-120 hours, to obtain sol (E). A film-forming fluxing agent is added to sol (E) and an alcohol solvent is added to adjust the silica solid content of sol to 3-6%. The pH of mixture is adjusted to 5-8 after seal-aging for 24-72 hours, to obtain the composite sol. An INDEPENDENT CLAIM is included for antireflection-coated photovoltaic glass consisting of a glass substrate and a film plated on the glass substrate. The glass substrate is ultra-white glass or ultra-white float glass for solar cell. The film is formed by coating the composite sol on the surface of glass substrate by liquid-phase coating method, and obtaining a silicon dioxide particle crosslinked network with a size of 10-100 nm, or a silicon dioxide particular crosslinked network and a metal compound and/or a fluxing agent doped into the network after heat-treatment. The film is 70-120 nm thick.