Abstract: To find out the appropriate potassium (K) ratio and time for maximum cotton yield, and the effect of K application on cotton yield, field experiments were conducted in 2012 on Lukou Experimental Station of Ezhou, Hubei Province. Potassium fertilizer was soil-applied in spilt on two of the three stages of cotton growth: before transplanting (A), squaring period (B), and peak bloom stages (C) of cotton, and then the treatments were: before transplanting and at squaring period (marked AB), before transplanting and at peak bloom stages of cotton (marked AC), and at squaring period and peak bloom stages of cotton (marked BC); and four application ratio rate by two times were 2:1, 1:1, 1:2 and 1:3, respectively. Fertilizer K application amount was uniform throughout all treatments. The results showed that, the highest seed index and bolls per plant were obtained at BC regime. Higher boll weight, lint percentage and fruits branch per plant were got for AB than that of AC treatment. For AC regime, the yield components of cotton was not the best, but the highest seed cotton yield was obtained. The highest yield components of cotton were got when the ratio of K application was 1:2. So, cotton demand for potassium in transplanting period (A) was less, but essential. Squaring period (B) and peak bloom stages (C) of cotton were the biggest potash demand period, and also the peak period of reproductive growth. It was significant effect on cotton yield to applied fertilizer K before transplanting and at peak bloom stages of cotton as treatment AC, and appropriately increasing the K application rate at peak bloom stages of cotton as a ratio as 1:2.