In order to lay a theoretical basis for soil testing and fertilization of cotton in the Northwest China planting region，Yangtze River planting region and Yellow River planting region，the scattered experimental data integration method，arcsine-log calibration curve and the nutrient balance-soil fertility difference subtraction method were employed to study the rich-lack index(RLI)of soil available potassium(SAK)and the recommended potassium fertilizer application rate(RPFAR)for cotton in these three major planting regions of China. The results showed that the RLIs of SAK in these three regions could all be divided into five levels. The RLIs of SAK for cotton in the Northwest China planting region for the 1st to 5th level were ≥418，166-418，111-166，80-111 and <80 mg/kg，respectively. The RLIs of SAK for cotton in the Yangtze River planting region for the 1st to 5th level were ≥357，128-357，81-128，56-81 and <56 mg/kg，respectively. The RLIs of SAK for cotton in the Yellow River planting region for the 1st to 5th level were ≥213，129-213，102-129，85-102 and <85 mg/kg，respectively. The critical soil test values of SAK in the above three major planting regions were 166.0，127.2 and 128.4 mg/kg，respectively. When the targeted yield of seed cotton was 2.5-9.0(ginned cotton，1.0-3.6)t/hm² and the seasonal potassium utilization was 50%，RPFARs for the 1st to 5th level soil from high to low were 0，30-108，60-216，90-324 and 120-432 kg/hm²，respectively.