Lactic acid has a unique complexation constant for nickel. More than 97% of the nickel ions in the electroless nickel plating solution of the lactic acid-nickel ion system are in the complex ion state, and the free nickel ion content is less than 3%. Therefore, lactic acid is commonly used for electroless nickel plating. One of the complexing agents. Compared with other complexing agents, lactic acid has strong stability in the plating solution, which can effectively control the deposition rate to ensure uniform and fine plating and stable plating solution. In addition, it is also very effective for suppressing the precipitation of nickel phosphite generated during the electroless nickel plating operation. Lactic acid has excellent synergistic ability, and can form binary or multi-component complexing agent with various complexing agents such as sodium citrate, malic acid and succinic acid, further satisfying the demand for complexing agent in the electroless nickel plating industry.