Abstract: This paper deals with the K-nutrition for chinese cabbage and its physiological mechanism. The results from sandy culture experiment indicated that K supply can enhance both the contents and the amounts of N. P in chinese cabbage by promoting root growth, activity of dehydrogenase in root and activity of nitrate reductaes in leaf,and increasing dry matter production by enhancing Chl. content and promoting stomatal conductance (CS). transpiration rate (TR), net photosynthesis rate (PN) as well as transplration efficiency. And from the field experiment, it can be obtained that K fertilization increase the levels of endogenous phytohormones in chinese cabbage as well as regulate their balance as decreasing the ratios of ZT/ABA and IAA/ABA, which is functional for head production.The experimental results also indicated that potash sulphate affects on these physiological mechanisms more efficiently than potash chloride does, which is the reason why chinese cabbage can yield more with potash sulphate applied at the adequately-high rates of K fertilization.