The relation of oil removal rate from aluminium alloy surface and NaOH concentration, solution temperature, soak time and stirring intensity was studied. With orthogonal test, the process conditions were optimized. In test conditions, the order from big to small of influence factors is:the reaction temperature,soak time,NaOH concentration,stirring intensity. The optimized process conditions are as follows: solution temperature 60 ℃, soak time 20 min, NaOH concentration 90 g/L and stirring intensity 400 r/min. Under the optimized process conditions, the oil removal rate reaches above 99%.