[Objective]To explore the suitable potassium level of high yield for conventional cotton.[Method]Taking the transgenic cotton Hanmian 802 as test material, different potassium fertilizer treatments(0,120,180,240 and 300 kg/hm2 ) were setted,the effects of potassium fertilizer on verticillium wilt diseased plants rate and yield of cotton were studied under the best fertilizer ( base fertilizer and topdressing during the blooming period each accounted for 50％) and the optimum planting density (52500 plants/hm2) conditions.[Result]Hanmian 802 was sensitive to demand for potassium fertilizer ,potassium fertilizer can effectively reduce the occurrence degree of cotton verticillium wilt ,significantly promote the total cotton boll number and boll weight,significantly increase the yield of cotton,and the effect increased with the amount of potassium increased.Among them,the amount of potassium was less than 240 kg/hm2 ,the different effects of different potassium treatments were significant . When potassium fertilizer >240 kg/hm2,continuously increase the fertilization level,the synergistic effect was not obvious.[Conclusion]Under the condition of this study,the economic fertilization amount of potassium chloride for Hanmian 802 was 240 kg/hm2 ,cotton verticillium wilt infection rate was 15.0％,64.29％ lower than CK,the yield was 4630.4 kg/hm2,increased by 35.00％ compared with CK under the treatment.