Abstract: To reveal the responses of different tobacco genotypes to low potassium stress, flue-cured tobacco cv. K326 (low potassium content genotype) and GK8 line (high potassium content genotypes, bred by the research group of this study) were used as experimental materials, the effects of low potassium stress were investigated with water culture experiments. The results showed that under low potassium stress, the plant height, dry weight of roots and aerial part of the two genotypes were inhibited, and the difference of K326 between normal potassium and low potassium treatments was more obvious than that of GK8, which indicated that K326 was more sensitive. Under low potassium stress, the volume and vigor of roots of the two genotypes were decreased, however those of GK8 were significantly higher; chlorophyll content, cation exchange capacity, soluble protein content, nitrate reductase activity, ATPase activity decreased more significantly in K326.