Abstract: The law of potassium release was investigated with four kinds of lowmolecularweight organic acids at 0.05mol/L each extracting four fragments of purple rocks and two purple soils for 3000 hours. The results indicated that lowmolecularweight organic acids could obviously accelerate potassium release from the soils and purple rocks, and the release rates were far quicker than that extracted by pure water under the same conditions, the accumulative amount of potassium release of the former was 0.3～15.2 times larger than that of the latter. The ability of four kinds of organic acids to extract potassium in four soils (or rocks) was in the order of oxaliccitrictartaricmalic acid. Five common kinetic equations were used to simulate the potassium release in 3000 hours of J2s and J3s purple mud rocks and greybrown purple soil. The results showed that all the equations except the onestep diffuse one fit well (r=0.5988～0.9966) with the process of potassium release, and the Double Constant Equation gave the best results. The constant b could be used for estimating the rate of potassium release.