By analyzing the dynamic change of cultivated lands in Zhangye City, it was found that behind the change there were two groups of driving forces: natural factors and social economic factors. Of the former, water resource were the major component. With the method of principal component analysis, the social economic factors could be summed up as development of economy, growth of population and advancement in agricultural technology. In the end, in response to different driving forces, different specific countermeasures were broght forth.