The K supplying potential of 11 main soils in China was evaluated comprehensively with pot experiment of bio-depletion of soil potassium and chemical methods. Results were summarized as follows:stage of the minimum value appearance and amount of soil exchangeable K varied with soil type after soil potassium depletion. The soil exchangeable K also has "utilization ratio" or "availability degree".Its minimum value is one of the important characteristics of soil K supplying potential. As reaching the minimum value the non-exchangeable K increases again with the increase of the potassium depletion time, and finally, approaches or overtakes a level of pre-depletion. The results were suggested that potassium which could not be extracted by boiling in 1 mol/L HNO₃ was released largely and absorbed by plants mainly. It would not be mineral K but nonexchangeable K.The closest correlation between the soil available K extracted by cold 2mol/L HNO₃ and the content of K absorbed by plants was revealed by all of the test methods. The procedure of this method is simple and easy to operate. It is applicable to test soil K of upland and paddy field. The K supplying potential of 11 main soils of China were classified preliminary based on the content of soil available K and its minimum value.