Accumulation of Nitrogen,Phosphorus and Potassium in different growth period of Long_day were analyzed,and the pattern of the nutrient demand was established.The result showed that 5.78 kg of Nitrogen,2.02 kg of Phosphorus and 10.0 kg of Potassium were needed when forming 2 560 kg onion in 667 m².This can be used as a guide for onion fertilization.