The biological potash fertilizers (bio-K fertilizers) are the plants which can strongly absorb potassium from soil and accumulate K relatively high in its tissue. To investigate the mechanism of K-enriching carpacity of bio-K fertilizer and its influence on crop yield, three xypical plants-rice straw sunflower (fresh plant) and Alterndntherd philoxeroides (Mart) Griseb were used in pot and field experiments.It was found that the yield increased significantly by applying the bio-K fertilizers to potassium deficient soils. The average percentage increased was 17.5±8.2% for rice grain and 11.7% for lint cotton as compared with control However, at equal amount of K level applied,there was no significant difference in yield among all treatments of potassium chloride and bio-K fertilizers, it indicates that the K-supplying capacity of bio-K fertilizers is similar to that of KCl. In the terms of absorption rate of nonexchangeable-K by plants tested, the capacity of K accumulation waS high during its growing stage. Based on the total potassium absorbed, 68-76% of nonexchangeable-K was taken up by rice plant and 40-62% of that by sunflower (seedlings, 57 days). As to Alzernantlzera philoxeroides, the K⁺ concentration both in higher and lower solution can be recovered by 97% and 71-90% respectively, it seems that the roots of Alternanther a philoxeroides have a strong affinity to K⁺.The K⁺ in soil could be mantained by organic matter supplied as bio-K fertilizers. As a result, the loss of K⁺ from soil was decreased by 40%, this benefit was more markedly for sandy soils.Data from long-term experiment for four years showed that the K in soil appeared to be somewhat depleted, as compared with its origin content, this unbalance is mainly due to the K removed by crops excessing the K supply (90 kg K₂O/ha per year). However, the K consumed could be partly returned to soil by the use of bio-K fertilizers.