Abstract: In order to analyze the physiological mechanism behind the promotional effects of carbon-nano sol on the potassium absorption by tobacco, sand culture experiments and non-invasive micro-test (NMT) were used to study the effects of carbon-nano sol on K⁺ channel gene expressions, root K⁺ fluxes, potassium uptakes and accumulations by four tobacco varieties, RG17, Eyan 1, Yunyan 87 and Zhongyan 100. The results showed that carbon-nano sol could promote the expression of K⁺ influx channel gene and K⁺ influxes and inhibit K⁺ effluxes, however the responses of K⁺ channel gene in different varieties and different parts of tobacco were different. Under the carbon-nano sol treatment, the expressions of K⁺ efflux channel gene NTORK1 in RG17, Eyan 1, Yunyan 87 and Zhongyan 100 decreased by 31.1%, 59.9%, 25.6% and 32.0% respectively, as compared with the control. the expression of NKT1 in the roots of Eyan 1 and Yunyan 87 significantly increased by 210.6% and 130.9% respectively. Carbon-nano sol treatment raised the K⁺ fluxes of the roots of each tested leaf variety. Compared with the control, the K⁺ influxes of RG17, Eyan 1, Yunyan 87 and Zhongyan 100 increased by 38.17, 39.71, 13.96 and 8.61 pmol·cm^-2·s^-1 respectively under the carbon-nano sol treatment. In addition, the potassium accumulations in Eyan 1, Yunyan 87 and Zhongyan 100 increased by 18.6%, 15.6% and 46.6% respectively, as compared with the control. In conclusion, by regulating the expression of K⁺ channel gene in the root system, the carbon-nano sol could enhance the uptake of potassium by the root system and promote the accumulation of potassium in tobacco. There were significant differences in the responses of different tobacco varieties to the carbon-nano sol treatments.