Effects of the foliar fertilizer on the uptake of potassium (K), as well as translocation and distribution among different position of tobacco leaf were studied under lack of K conditions. In order to study the suitable contents and the critical value of nutrient deficiency of K on tobacco under different levels of K, hydroponic experiments were used. After treatments of 30 g·L-1 KNO3 to the median leaves of tobacco lacking in K, leaf samples were collected during different periods, respectively. Dry weight and nutrient contents were measured. In addition, the relative contents of K in different tissues of veins or petiole were determined by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results showed that the growth of tobacco was significantly affected by K content (< 4 mmol·L^-1) and that the critical value of tobacco K deficiency was 11.5 % mg·kg^-1. 0.04 day after the foliar fertilizer treatments, the K was transported to different parts of the leaves with high speed. The concentration of K in the superior leaves was significantly higher than that in the inferior leaves, indicating that K was preferentially transported to superior leaves. EDS analysis showed that K tended to be transported to tender meristems, and could also be transported through phloem and xylem to superior leaves and inferior leaves simultaneously. K was distributed mainly in the parenchyma in the tobacco leaves. The relative contents of K in the adaxial epidermis, adaxial parenchyma, vascular tissue, abaxial parenchyma and abaxial epidermis of the superior leaves, median leaves and inferior leaves were increased significantly, with the vascular tissue increasing most.