An impregnating agent for winding reinforcement medium-alkali glass fiber direct yarns comprise a coupling agent, a lubricant, a film forming agent, a surfactant, a pH adjusting agent and deionized water, and the impregnating agent comprises 5-14 mass% of a impregnating agent solid, and the balance of water; the coupling agent adopts a silane coupling agent; the lubricant adopts a water-soluble PEG lubricant; the film forming agent is an organo-silicone modified epoxy emulsion, aqueous polyester emulsion A and aqueous polyester emulsion B blend, the molecular weight of polyester in the above aqueous polyester emulsion A is 800-3000, and the molecular weight of polyester in the above aqueous polyester emulsion B is 4000-10000; the surfactant is a cationic surfactant; the pH adjusting agent is an acid; and the pH value of the impregnating agent is 2-10. Direct yarns produced by adopting the impregnating agent have good compatibility with target resin, have good permeability, and make products have good mechanical performances and meet standard requirements.