Abstract: The effects of N, P and K application on stem length, stalk width, yield of welsh onion(Allium fistulosukm) and benefit of the fertilization were studied in the field by using the 311-A optimum regression design of supposed saturation. The results show that the optimum N, P and K application amounts for the maximum stem length of welsh-onion (92.88 cm) are N 371.30，P2O5 157.50，and K2O 309.58 kg/ha；the optimum application amounts for the maximum stalk width of the crop (1.769 cm) are N 350.63, P2O5 157.50, and K2O 225.00 kg/ha; and those for the maximum yield (55805.06 kg/ha) are N 394.08, P2O5 193.62，and K2O 225.00 kg/ha. The optimum N, P and K application amounts for the best fertilization benefit are N 391.35, P2O5 192.97, and K2O 225.00 kg/ha. The best fertilization benefit is about 136865.6 Yuan/ha with a yield of 55802.74 kg/ha.