Abstract: There are medium contents of total K and lesser medium contents of available K in the paddy soils developed from pruple soils so that soil K is not sufficient for potassium requirement of crops in short. Mineral K accounts for 76. 95% of potassium uptaken by crops, while slowly available K and available K only accounts for 12. 24% and 10. 84%, respectively. The release of mineral K in the soils gradually decrease with prolonging of time and significantly increase with decreasing of size of soil particle. The accumulative releasing capacity of mineral K during 80 min is 1. 5-2. 0times of slowly available K, and releasing capacity in 80 min can reach 0. 8-8. 8 mg/(kg.min). The formation of soil available K may tend towards constant with extending of time. The inconsistency of sequences of releasing capacity of mineral K and formating capacity of available K in various soils insults from their mechanisms and soil properties. The releasing proccesses of mineral K and the formalating proccesses of available K can fit by the Elovich equation, in which b values can express the rate of these proccesses.