The “3414” incomplete orthogonal regression design was adopted to explore the effect of nitrogen，phosphorus，potassium fertilizers combined application on flax growth.The changes of economic characters，yield，growth rate，fertilizer contribution rate，input-output ratio in three fertilization gradients were studied and the flax yield was fitted with fertilizer efficiency model.The result showed that low and medium nitrogen，phosphorus，potassium promoted the economic characters，and the yield increased by 4.95%～24.07% under nitrogen，phosphorus，potassium fertilizers combined application.It was found that the flax yield increased firstly and then decreased with the increase of fertilizer application. The yield was the highest when nitrogen(N)，phosphorus(P2O5)，potassium(K2O) were applied at 75，67.5，72 kg/hm²，respectively.Potassium had a greater contribution than nitrogen and phosphorus，and high phosphorus led to a reduction of yield.The recommended maximum fertilization rate under the experimental conditions is:N 69.1 kg/hm²，P2O5 51.5 kg/hm²，K2O 63.4 kg/hm²，and the best fertilization rate is:N 39.6 kg/hm²，P2O5 26.5 kg/hm²，K2O 25.7 kg/hm².