The effects of potassium （K） application rates on the yield, fiber quality and K fertilizer use efficiency of three hybrid cotton varieties （Jin102, Xiangzamian8, Siyang328） were studied in field experiment. Fertilizer rates of K2O 135 and 270 kg/hm2, representing 1x and 2x recommended K rates, were applied, no application of k fertilizer as the CK. The results show that the lint yield increased 39.13%-57.48%with potassium application, highly significantly. Al yield components of the three hy-brid cotton varieties increased with the increase of K application amounts. The bol number per plant, single bol weight and lint percentage were increased by 14.24%-40.29%, 3.59%-15.51% and 0.16%-4.89%, respectively, and the fiber length and specific strength also increased with the increasing K application amounts, showing no significant influence on Micronaire. When the K application amounts increased from 135 to 270 kg/hm2, the partial factor productivity （PFPk） reduced by 45.93%-48.01%, and the agronomic efficiency （AEk） reduced by 37.1%-42.9%. The PFPk and KE （K efficiency coefficients） of S328 were the highest among the three varieties, which also showed the strongest resistance to low potassium stress, and with no potassi-um fertilizer application （K0）, the lint yield of S328 was 5.54% and 11.19% higher than that of X8 and J102. The AEk of J102 was the highest, and its reward of K fertilizer was the greatest among the three varieties.
