The field experiment that carried out in Bai San soil(Paddy soil derived from yellow brown soil) in Jing-men showed, after rice straw overlaying the wheat farmland, there was significant alteration on the content of available potassium in soil. In addition, the rice straw overlay could improve the physical and chemical properties of the soil, and increase the amount of water content in soil, regulate the soil temperature. Compared with the check treatment, the soil covered with rice straw could increase the valid seed and the weight of seed in wheat obviously, the yield increased from 2899.5kg/hm~2 of uncovered to 3558kg/hm~2 covered. The 84% potassium in the rice straw was poured out within only 3 hours. But after 4 months in field trial, 90% potassium entered the soil. Therefore, the returning rice straw to farmland is an effective method to alleviate the fertilizer resources in potassium shortage, deserving expansion application in the soil region that lacks potassium.