Based on the culture experiments, the mechanism of K mobilization from minerals has been studied with flow extraction technique by simulating the types and the concentrat ions of organic acids that plant roots excretes under P def iciency The results showed that organic acids significant ly stimulated K release from minerals, and the release of K increased with the concentration of organic acids Moreover, the mobilizing ability was closely correlated to the type of the organic acids and minerals The release of K from feldspar and muscovite was simulated by a transfer function model The simulated data was correlated with the measured data It indicated that the transfer function model is useful in studying mobilization of structural K in K-bearing minerals.