The invention discloses an impregnating agent for coating the glass fiber surface. The impregnating agent is prepared from, by weight, 30-40 parts of vinyl resin emulsion, 20-30 parts of polyurethane emulsion, 0.5-2 parts of urine butanone, 3-5 parts of a coupling agent, 0.5-2 parts of modified organo-silicone emulsion, 0.5-1 part of a pH regulator, 0.5-1 part of acid-proof and alkali-proof agent dispersion liquid, 0.5-2 parts of a lubricant, 0-0.5 part of an antistatic agent, 0.5-1 part of a collecting agent and a proper amount of deionized water. By adopting the components of the impregnating agent, yarn has high strength and a good permeating effect in the impregnating treatment process. According to the impregnating agent, by using the high-performance lubricant and introducing the collecting agent, an excellent weaving effect is achieved while the good permeating effect is guaranteed; with the long-chain alkylphenyl modified organo-silicone emulsion, the usage temperature of glass fibers can be raised, water repellency is achieved, and dust accumulation caused by vapor and corrosion to glass fibers are reduced; as the acid-proof and alkali-proof agent is designed and added in the formula, the acid and alkali resistance of glass fibers is improved, and the strength loss under the acid and alkali conditions is obviously reduced.