Effects of potassium fertilizer application rates on crop yield, economic benefit and soil potassium content were studied in a cotton-garlic intercropping system by a four-year located experiment. There were four treatments, CK (K2O 0 kg/hm2), K90 (K2O 90 kg/hm2), K180 (K2O 180 kg/hm2) and K270 (K2O 270 kg/hm2). The results showed that K fertilizer application significantly increased cotton yield by 18.4%-72.7%. Lint cotton yield increased with the increase of potassium application rate, but no significant difference was observed between K180 and K270. The bolls and boll weight were significantly increased compared with CK. Potassium application increased garlic bulb and bolt yield by 10.1%-64.2% and 8.7%-93.3%, respectively, compared with CK. K270 had the highest bulb yield in 2016. Soil available K content increased in the 0-20 cm soil layer with the increase of potassium application rate but no significant difference was observed among treatments in the 60-100 cm soil profiles. After four-year fertilization, water-soluble K content of K90, K180, and K270 was increased by 13.6, 20.1, and 26.1 mg/kg, respectively; non-specifically adsorbed K content was increased by 10.4, 19.6, and 53.4 mg/kg, respectively; and non-exchangeable K content was increased by 34.3, 53.9, and 140.1 mg/kg, respectively compared with CK. The overall results suggest that the appropriate potassium application rate ia K2O 180 kg/hm2 for cotton and K2O 270 kg/hm2 for garlic in the cotton-garlic intercropping area.