Field trials were conductded by using the regression design of quadric orthogonal rotationin southern ningxia hilly area.By means of establishing mathematical model, this paper analysisedthe input of N, P₂O₅ and seeding rate.The relationship among N, P₂O₅,seeding rate and yield wasset up,with which the optinal medel for flax cultivation vvas set out.The model gave the inputamount of fertilizer and seeding rate according to rainfall style.They were that:in ordinery rainfallstyle,N is inputed by 96.4kg/hm², P₂O₅ 92.7kg/hm²,seeding rate:55.2kg/hm², and the yieldwould be 1921.3kg/hm², Under the drought style: N:101.2kg/hm², P₂O₅:102.6kg/hm², seedingrate:56.4kg/hm², and the yield would be 1 568.2kg/hm².The optinal model would be very signifi-cant for improving flax yield in practice.