Abstract: In this paper, the effect of potassium fertilizer was studied about winter wheat and summer maize rotated in sandy Chao soil field. The results showed that with increasing of the applied of potassium fertilizer, the yield of winter wheat became higher. The efficiency is the best when the amount of applying potassium fertilizer is 150kg/hm2 and the ratio of basic to dressing is 5: 5. It can increase the yield 822.7 kg/hm2, or increase the money 724.1 yuan/hm2, the ratio of import to export is 2.42. In the maize yield, the optimal rate of potassium fertilizer is 150kg/hm2 and the optional ratio of basic to dressing is 5:5 at which the highest ratio of import to export is 2.52, and it can improve the yield 1368.4kg/hm2, or the money 1281.7 yuan/hm2. In the system of winter wheat and summer maize rotation, when the optimal rate of potassium fertilizer is 150kg/hm2 and the optional ratio of basic to dressing is 5:5, the potassium fertilizer should be applied respectively in wheat and maize. When the optimal rate of potassium fertilizer is 3000kg/hm2 and the optional ratio of basic to dressing is 5:5, the potassium fertilizer should just be applied respectively in wheat.