To determine the optimal potassium application rate for high-quality cigar filler tobacco in the Jinsha River Basin of Yunnan and to improve the yield and quality of tobacco leaves, this study used ‘Yunxue 39’ as the material and investigated the effects of different potassium application rates on the growth period, botanical traits, agronomic traits, disease resistance, appearance quality, chemical composition, and yield of cigar filler tobacco in Suijiang County, Zhaotong City, Yunnan Province. Three treatments were set up for the experiment, including T1 ( potassium application rate of 468 kg/hm², N:P:K = 1 : 1.15 : 2.6 ), T2 ( potassium application rate of 630 kg/hm², N:P:K = 1 :1.15:3.5 ) and local conventional fertilization CK ( potassium application rate was 546 kg/hm², N:P:K = 1 :1.15:3 ). The results showed that the incidence of disease in tobacco plants decreased with increasing potassium application. The T2 treatment had the lowest disease incidence during the field period. Different potassium application rates had no significant effect on the main growth stages and agronomic traits of tobacco plants during the field period. However, with increasing potassium application, the stem circumference, plant height, and leaf area index of the tobacco plants increased to varying degrees. The botanical traits and appearance quality of the T2 treatment were significantly better than the other two treatments, and the moisture content of the tobacco plants was moderate. Compared to the CK and T1 treatments, the fresh tobacco leaf yield of the T2 treatment increased by 2773.50 and 3639.00 kg/hm², respectively, and the output value increased by 16013.00 and 18268.50 yuan/hm², respectively. After curing, the dry tobacco leaf yield of the T₂ treatment increased by 6.50% and 13.72% compared to the CK and T1 treatments, respectively. The proportion of grade 1 tobacco leaves in the upper, middle, and lower parts of the T2 treatment was significantly higher than that of the CK and T1 treatments. With increasing potassium application, the total sugar, total nitrogen, water-soluble chlorine, potassium oxide, K/Cl, reducing sugar/total alkaloid, and total nitrogen/total alkaloid in cigar tobacco leaves gradually approached the domestic and foreign high-quality of cigar filler tobacco. Among the three treatments, the chemical composition of the T₂ treatment was the most stable, particularly in terms of potassium oxide content, which was closest to that of high-quality cigar filler tobacco from Nicaragua. In conclusion, the T2 treatment is the most suitable potassium application rate for high-quality cigar filler tobacco in the Jinsha River Basin of Zhaotong.