Abstract: To explore the suitable nitrogen, phosphorus and potassium fertilization on winter sowing flax in southern Yunnan, a field experiment was carried out with“3414”test scheme in Menghai County, Yunnan Province to study the relations between the main economic characters, straw yield and nitrogen, phosphorus, potassium fertilizer rates. The results showed that the reasonable use of nitrogen, phosphorus and potassium fertilizer could improve the main economic characters such as plant height, technical length, stem diameter, grains per capsule and thousand kernel weight of fiber flax, significantly increased straw yield and seed yield. The positive effect of nitrogen on straw yield and seed yield was the largest, followed by that of phosphate, while that of potash was the minimum. Based on the analysis of nitrogen, phosphorus and potassium fertilizer rates and the ternary quadratic model of straw yield, the best yield of winter sowing fiber flax was 7605 kg/hm2 in Menghai County, and the best corresponding fertilizer amount was pure nitrogen 272.86 kg/hm2, phosphorus pentoxide 77.48 kg/hm2, and potassium oxide 128.67 kg/hm2, with the balanced nutrient ratio of 1.00: 0.28: 0.47.