Abstract: This experiment is conducted to study effects of potassium nutrition on growth of cotton through water culturing. The main results were as follows:.compared with CK, the growth of cotton was promoted obviously, and stem height , the leaf area were all increased because of boosting of K concentration in nutrient properly. Under this trial conditions, a cotton high growth assumes "S" the shape curve growth is the initial period slow, intermediate stage quick, later period also is slow, until stops growing. The velocity of stem growth assumes the single apex curve variety.The sufficient K nutrition also promoted the cotton root system growth, the activity of roots, the total absorption and active absorption area were increased, but there is discrepancy in difference varieties, low potassium surpasses high potassium and CK about "XinLuzao 13" , "ZhongMian36" is more superior along with the K concentration increasing.The content of Chla, Chlb and Chl were all increased with the improving of K in nutrient,but high potassium was not propitious to the synthesis of chlorophyll, two varieties cottons display consistently, the content of chlorophyll of low potassium is more than that of high potassium,which is more than that of CK in this experiment.