Abstract: Six years' location investigations and tests on soil K dynamics in the rice growing areas of Zhangye City, which locates in the central part of Hexi passage,showed that soil Kcontents of different type of soil are all decreasing,the decreasing rate is in relation to soil type,amouns of N,P and Zn fertilizers applied.Based on long-period tests the optimum amount of K fertilizer application was got. This provided the base for rational application of potassium fertilier to rice.