Abstract: Quantitative analysis of the transla tional processes of potassium in water-soil-azolla system was carried out by using tracer technigue so as to suggest a cycle model of potassium in this system.Results of the study showed that, when azolla was cultivated in the paddy field, the potassium source enriched by azolla essentially depended oa the potassium transport and reaching dynamic equilibrium between water-soil cycle. Under condition of complement of potassium from irrigation water and rain, the trace result showed that the potassium enriched by azolla mainly came from those sources and from soil a fittle. Therefore, azolla may be a prospective biological potassium source.