Objective In order to obtain Ni-P coating with excellent performance, the ternary complexing agent for medium temperature was optimized. Methods By selecting lactic acid, glacial acetic acid and citric acid as complexing agents, using plating speed and phosphorus content as evaluation indicators, the effect of sodium phosphate, lactic acid, glacial acetic acid and citric acid concentration on the plating speed and phosphorus content was studied through designing L9( 3 4) orthogonal experiments. Results Considering the plating rate and phosphorus content, the optimal ternary complexing agent system was determined as follows: lactic acid 20 mL/L, glacial acetic acid 15 mL/L and citric acid 10 g/L. The plating speed was 6. 4 milligram per hour and phosphorus content was 8. 8wt% in this optimal system. Conclusion The results showed that even and compact Ni-P coating with good adhesion could be obtained in the optimized complexing agent system.