Abstract: The sequential extractions combined with conventional methods were used to study the availability of K adsorbed by clay minerals and the profile distribution under longterm fertilization of brown soil, with a maizemaizesoybean rotation. Results showed that the contents of K and the proportion in total K on arable layer presented as follows: i＞e＞p. Contents of p, e and i sites K with chemical K fertilizer application and no K fertilizer application decreased. And organic manure with K fertilizer application could remain the amount of K at a higher level. Correlation analysis indicated positive correlation between psite K, esite K and exchangable K, and the correlation coefficient were 0.926*and 0.886*, respectively. A positive significant correlation was observed between psite K, esite K and the uptake of K by crops. And there was a highly significant correlation between i sites and the uptake of K by crops (r=0.963**). There was an extremely significant positive correlation among psite K, esite K and i site K. The tendency of contents of potassium were all changed with depth as follows: 0-20 cm＞20-40 cm.