Pinggu District of Beijing was selected for research on spatial difference between regions of different landforms in change in farmland acreage and trend of the changes. And the multi-factor regression method was used to analyze mechanisms driving the changes in the district as awhole and various regions of landforms. Results showed that: ①the changes in farmland acreage feature spatial discrepancy, high intensity and high rate; ②the main trend of the changes is the transition of farmland into orchards and followed by construction land; ③the analysis of driving mechanisms indicated that the driving forces vary from region to region different in landform, but all are the results of the joint effect of socioeconomic and natural environments, and among the form, human is the most important factor; and ④regardless of landform regions, quality and quantity of the cultivated land is not a driving factor of the change, suggesting that the transformation rate of cultivated land does not depend on change in quantity and quality of the land. It is, therefore, essential to intensify protection of quality farmlands and cultivated lands in some key agricultural regions.