Discussed Ni-P alloy plating process on aluminium substrate of electroless, used acid zinc directly under the condition of displacement to the feasibility of pretreatment and optimized the pretreatment process using the orthogonal experiment method. The experiments show that the high phosphorous nickel-phosphorus alloy coating can been got when the replacement time is 10 s, the HF concentration is 10 mL / L, the replacement temperature is 25 ℃ , OP emulsifier concentration is 20 mL / L. The thickness of the coating is about 38 μm, the hardness of the coating is about 503 HV, the combines of the coating with the aluminum substrates is well .