[Objective] To provide some bases for nutrient regulation of high yield maize, the effects of potassium fertilization on root vitality of a high yield spring maize were investigated. Potassium fertilization had application level treatment with two levels of 150 and 300 kg/hm² and application method treatment with levels of once-and-base fertilizer and postponed application.[Methods] A maize cultivar, Jinshan 27, was used as the test material. Its dry root weight, root vigor, activities of superoxide dismutase(SOD) and peroxidase(POD), and malondialdehyde(MDA) content were measured at each stage; root number and root width were measured at mature stage.[Results] Root dry weight at 300 kg/hm² application level was greater than that at 150 kg/hm², especially it was obvious in 0-20 cm layer before silking stage. The percentage of root weight at 20-60 cm was contrary, especially in milking stage. Root number increased at high application level, and also the biggest root width increased and proliferated deeper. At high application level, vigor, SOD and POD activities of root in all growth period increased, while MDA content decreased. Root weight of postponed fertilization at 0-40 cm soil layer was less than that of once-and-base fertilization method; while, the percentage of root weight at 0-20 cm soil layer was relatively great. Root number, the biggest root width and the layer with the biggest root width of postponed application was lower than that of the once-and base application method, and the differences of these indices between the two methods increased with the increase of soil depth. Root vigor and activities of SOD and POD of postponed application decreased; MDA content increased.[Conclusion] Once-and-base K application could improve the root growth of maize and especially the proliferation at deep layer was promoted; It also delayed the senescence of root. These effects were not observed, and moreover the contrary effects it were for postponed application.