The invention relates to an environmental-friendly water-soluble flux which is matched with lead-free solder; the environmental-friendly water-soluble flux comprises anhydrous citric acid, DL-malic acid, triethanolamine, modified polyvinylalcohol, polymethyl acrylate, vinyl acetate-ethylene copolymer powder, hydroxyethyl methyl cellulose ether, surfactant, benzotriazol, phenol and mixed solvent; the anhydrous citric acid, the DL-malic acid, the triethanolamine, the modified polyvinylalcohol, the polymethyl acrylate, the vinyl acetate-ethylene copolymer powder and the hydroxyethyl methyl cellulose ether are prepared into a complex active substance A through microencapsulated coating treatment; and the mixed solvent, the surfactant, the benzotriazol, the phenol, the modified polyvinylalcohol, the polymethyl acrylate and the complex active substance A are uniformly mixed by weight ratio to obtain the environmental-friendly water-soluble flux. The environmental-friendly water-soluble flux can effectively assist lead-free solder, particularly applicable to Sn-Ag-Cu lead-free solder, can enhance the solderability of the lead-free solder, can adapt to the high welding temperature requirement on the lead-free solder, has small action to the corrosion of lead-free solder alloys and little residue after welding, can be cleaned by water, has good welding point quality, clean surface and strong stability, and a dried circuit board has higher insulation resistance value.