Abstract: Maize may suffer a good many nature disasters and serious drought stress during its growth period. Drought brings about more output reduction than the sum of that caused the other nature disasters. Drought affects the process of physiology metabolizability, i.e., cell growth, photosynthesis, respiration, hormone and enzyme metabolizability, and the absorbability, transportation, translation, accumulation of water, mineral element and organic compound. Kalium ion is the most important osmotic regulation substance that can improve osmotic regulation of plant which increases plant resistance to drought. The kalium nutrition of plant is mostly derived from soil and root is a main organ for kalium absorption. The growth of root and its ability of gaining kalium affect the status of plant kalium nutrition to a certain extent. The ability of absorption and utilization of water is related to plant kalium nutrition closely. The lack of kalium could inhibit water and nutrition utilization in plant and root growth. Many researches regarding the osmotic stress on growth and physiology metabolizability have been reported, but few researches are reported regarding the effects of osmotic stress on kinetics parameters of K+ uptake of root. Three hybrid varieties with different drought resistant abilities were used as experimental materials. We used 26% Polyethylene glycol(PEG) (MW4000) to cause osmotic stress to study the effects of osmotic stress on root vigor and kinetics parameters of K+ uptake of maize seedling. The results were as follows: the K+ uptake rate of maize seedling root can be described by Michaelis-Menten kinetics equation. Short-term (in 24hours) osmotic stress promoted the growth of root, increased root vigor, inspired NR activity and enhance the appetency between root and ion enhanced (Km value of K+ uptake decreased) . High drought-resistant variety had more positive response to short-termosmotic stress than that of low drought-resistant variety. After 48 hour, osmotic-stress inhibited the root growth; decreased root vigor, reduced NR activity, and depressed the appetency between root and ion (Km value of K+ uptake increased) . The stress caused by the long term osmotic stress on high drought-resistance variety was small and Km value increased slightly, while the damp on low drought-resistant variety was more serious, and Km value increased more. There was a significant correlation between Km value of K+ uptake and number of roots, root weight, absorbs area of root, root vigor and NR activity. The Km value of K+ uptake can be used as an index for the drought-resistant ability of plants.