Abstract: In order to reveal the physiological basis of potassium absorption promoted by nano-carbon sol, a water-culture experiment and an enclosed sterile culture experiment were carried out. The effects of nano-carbon sol application on the physiological characteristics of root system, potassium absorption and related gene expression level of flue-cured tobacco cv. K326 and cv. Hongda were studied. The results showed that at the concentrations of 10-20 and 5-10 mg/L, nano-carbon sol significantly promoted the growth of root system, increased the shoot and root biomass and improved potassium absorption and accumulation in leaves of K326 and Hongda. With the increase of nano-carbon sol concentration, the vigor, absorbing area, cation exchange capacity and soluble protein content of root system of K326 and Hongda increased first then decreased. The expression levels of K⁺ channel gene NKT1 and K⁺ transporter gene NtHAK1 in K326 and Hongda increased significantly, which promoted the potassium absorbing ability of root system.