The invention discloses an aqueous-phase synthesis method of chlorpyrifos by using trichloro-acetic chloride as an initial material. The method comprises steps of: reacting trichloro-acetic chloride, acrylonitrile, orthodichlorobenzene and a compound catalyst to obtain a 3,5,6-Trichloropyridin-2-ol sodium crude product; adding the 3,5,6-Trichloropyridin-2-ol sodium crude product into a reaction kettle with water, a catalyst and alkali, heating for reflux for 3 h, standing to separate out a solvent, and cooling, crystallizing and filtering an aqueous-phase to obtain the 3,5,6-Trichloropyridin-2-ol sodium; and adding water into the reaction kettle, adding a dispersing agent, 3,5,6-Trichloropyridin-2-ol sodium, ethyl chloride and a catalyst with stirring, reacting, cooling, crystallizing, washing and conducting suction filtration to obtain a chlorpyrifos active compound product. The invention employs trichloro-acetic chloride as the initial material to produce high-purity 3,5,6-Trichloropyridin-2-ol sodium, which is used directly as a raw material for the synthesis of chlorpyrifos. The sodium alkoxide produced by the method does not require refining, purifying or drying; water is used as the medium; and reaction materials are added at once for synthesis of chlorpyrifos. The method has advantages of simpleness, easy operation, environmental protection, energy saving, increased product yield, and improved product purity.