Abstract: 【Objectives】The study on the right rate and right time of potash (K) application is the base for scientific use of fertilizers in main cotton areas.【Methods】 Field experiments were conducted successively two years in Shandong, Hebei and Xinjiang provinces. The treatments of K2O rate experiments were: 0, 30, 60, 120, 180, 240 kg/hm2 in Shandong Province, 0, 37.5, 75, 150, 225, 300 kg/hm2 in Hebei Province, and 0, 18.75, 37.5, 75, 112.5, 150 kg/hm2 in Xinjiang Autonomous Region. The treatments of K application time experiments in three locations all included: Control (no K), all K applied basally, 50% basally and 50% topdressing at flowering stage, topdressing 50% at bud stage and 50% at boll stage, topdressing 50% at bud stage and 50% at boll open stage, topdressing 50% at flowering stage and 50% at boll open stage.【Results】 The K application rates had no significant effect on the fiber quality, but on the yield and economic profit of cotton production. Potassium was mainly accumulated by aboveground cotton plants after flowering stage with the percentages of 54%-62%, 70%-73% and 49%-67% of total K accumulation during the whole growth period in the trials of Shandong, Hebei and Xinjiang, respectively. Potash application produced more lint cotton yield and economic benefit than K omission plots. The effect of potash rates on lint yield was more obvious in 2013 than in 2012 and the effect of potash rates on lint yield in different locations was XinjiangShandongHebei. The K2O rate for maximum yield was 142, 240, 174 kg/hm2 and for optimum economic yield was 136, 212, 150 kg/hm2, respectively. Compared with control without K, some fiber quality indices were affected by K application, but there were no significant difference between potash rates. When no straw returning, in Shandong and Hebei, annual application of K2O 180 and 150 kg/hm2 could sustain apparent soil K balance, but in Xinjiang, all the experimented K2O rates resulted in negative balance. The right time of potash application was topdressing 50% at bud stage and 50% at boll stage in Hebei and Xinjiang, and topdressing 50% at basal and 50% at flower stage in Shandong, which produced more lint yield, agronomic efficiency and economic benefit than other application time treatments. The length, strength and elongation of fiber were affected by the time of K application, although the effect varied in experimental years and locations, the length uniformity and macronaire value of fibre were not affected by application time.【Conclusions】Potash application rate has not affected the fibre quality, but the yield and profits of cotton production. The right rate and time of potash application in Shandong should be K2O 180-240 kg/hm2, with 50% basall and 50% topdressing at flowering stage; those in Hebei should be K2O 150-180 kg/hm2,topdressed 50% at bud stage and 50% at boll stage; those in Xinjiang should be K2O 112.5-150 kg/hm2, topdressed 50% at bud stage and 50% at boll stage.