Under pot culture conditions with no runoff and no leaching, the recovery rate of K fertilizer of the 10 major soil types of Guangxi were investigated and the values ranged from 79.0% to 93.8%, with an average of 87.5%. The correlation of the recovery rate of K fertilizer to soil available K after harvest was negative and very significant, and so was to soil cation exchange capacity (CEC). The calculation ways of the supply of soil K influenced the recovery rate of K fertilizer very greatly. The calculation of supply of soil K should be based on the variations of soil K status between planting and after harvesting and the buffer property of soil K, and so as the recovery rate of K fertilizer.