Potassium uptake and use efficiency are mainly related to the mechanisms of potassium uptake in root system, potassium translocation and distribution to harvested parts of crop. Therefore, we used single and double grafting technologies for two different cotton genotypes (103, a high potassium efficiency genotype; 122, a low potassium efficiency genotype) to clarify the main mechanisms of cotton high K use efficiency. Dry matter accumulation (TDW), root to shoot ratio (R/S), vegetative to reproductive ratio (V/R), harvest index (HI), K use efficiency (KUE) and K accumulation in the total plant (TK) were evaluated. The results showed that the TDW, R/S, V/R, HI, as well as KUE for the scions 103 in 103/122 were higher than those sum values of 103 and 122 in (103+122)/122, whereas those traits for the scions 122 in 122/103 were lower than those sum values of 103 and 122 in (103+122)/103, indicated the cotton K use efficiency is mainly related to the K translocation and distribution within above ground organs and tissues. Similarly, the TK for the scions 103 in 103/122 was higher than those sum values of 103 and 122 in (103+122)/122, whereas the trait for the scions 122 in 122/103 was lower than those sum values of 103 and 122 in (103+122)/103, in addition, when the scions were same in the double grafting, the TK for the 103 rootstock was higher than 122 rootstock under K1 condition, indicating that the K uptake efficiency was determined by the root and shoot genotypes. Therefore, more dry matter and K translocated into shoot and reproductive organs could be one of the main mechanisms of cotton high K-use efficiency.