【Objective】 Potassium is one of the essential mineral elements for normal growth of cotton and garlic. However, so far little has been reported on effect of controlled release potassium fertilizer on crops growth and soil potassium supply. The present study investigated effects of controlled release potassium chloride with or without the addition of sulfur as the alternates of potassium sulfate and potassium chloride on yield of cotton and soil available potassium content, in an attempt to provide a certain theoretic basis for rationalization of the use of potassium fertilizer. 【Method】 A three-year plot experiment was consecutively conducted in 2013, 2014 and 2015 under a cotton-garlic intercropping system in Northeast China. The experiment was designed to have six treatments: 1) basal application of potassium chloride (CK1); 2) basal application of potassium sulfate (CK2); 3) 50% of potassium chloride basal and 50% top-dressing at the full bloom stage (KClD); 4) basal application of potassium chloride with sulfur (KClS); 5) basal application of controlled release potassium chloride (CRK); and 6) basal application of controlled release potassium chloride with sulfur (CRKS), and three replicates for each treatment, and laid out randomly in plots separated from each other and isolated with cement boards. The K release of CRK in 25°C water and soil conditions was measured using the weight loss method in line with the “National Standard of the People’s Republic of China for Slow Release Fertilizer”. Samples of the soils and plants were collected for analysis of soil available potassium content, leaf SPAD value as well as net photosynthetic rate during cotton growth. Meanwhile, quality and yield of cotton were investigated, too. 【Result】Results show that the controlled release potassium chloride corresponded released K well in coincidence with the demand of cotton for potassium during its growth period. The contents of soil available potassium, leaf SPAD and net photosynthetic rate all increased in both Treatments CRK and CRKS after the full bloom stage especially at the initial boll-opening stage and harvest stage, as compared with the treatments of basal application of conventional potassium fertilizers (CK1 and CK2). The number of bolls per plant and weight per boll in Treatment CRKS increased significantly and hence the yield of lint did by 16.9%~30.9% over that of CKs, by 12.2%~16.1% over that of Treatment KClD and by 8.7%~10.4% over that of CRK. Treatment CRKS was also the highest in yireld of garlic bulbs and bolts, or 2.8%~27.9% and 4.8%~23.5%, respectively, higher than Treatment KCID and CRK. Treatment CRKS also significantly improved quality of the cotton, too, such as length, uniformity and specific elongation of lint fibre. After the three-year fertilization, the contents of soil water-soluble K and exchangeable K increased while the content of non-exchangeable K decreased in Treatment CRKS as compared with Treatments CK1 and CK2. 【Conclusion】 All the findings suggest that controlled release potassium chloride amended with sulfur is recommended to replace potassium sulfate and potassium chloride to achieve higher crop yields, higher soil K use efficiency, while improving crop quality under the cotton-garlic intercropping system.