Abstract: Under field production conditions, the experiment of effect of water- fertilizer Coupling on cotton yield under Surface Irrigation conducted with the cotton variety, Xinluzhong 9 of South Region of Xinjiang as stuff. The results showed that under Surface Irrigation conducted Water and fertilizer have the effect of increasing cotton yield，but when water and fertilizer supplies is excessive，the cotton yield will decrease. The relationship between cotton yield and number. of boll per plant is linear in the conditions. mathematical model for cotton yield and its main affecting factors water and fertilizer is established. Y=-1453.04+1.32703I+5.12236F-0.000211I2-0.005032F2-0.000263 I*F. The cotton yield per hectare will reach the top when W 2879 m3/ hm-2 and N 235kg/hm2、P2O5 143kg/hm2、K2O 56kg/hm2.