Abstract: It is necessary to carry out the study of spatio-temporal changes in cropland area during the important period of the grain-for-green policy (1999-2008) for food security and ecological security in China. The overall characteristics of spatio-temporal changes in cropland area were analyzed using gravity center model and regional comparison method based on the provincial-level cropland change data. The results showed that: the regional reducing order of cropland area was: west>east>central; the important period of the grain-for-green policy in China could be divided into two period: the early period was characterized by the sharp decline in cropland area and the movement of cropland distribution gravity center eastwards; the later period was characterized by the slow decline in cropland area and the movement of cropland distribution gravity center northwards; the movement of cropland distribution gravity center was largely affected by ecological de-farming, agricultural structural adjustment and expansion of construction land. The results implied that the expansion of construction land onto high quality cropland was an important factor restricting the overall productivity of cropland in China, and the movement of gravity center for cropland distribution northwards might reduce the effectiveness of the grain-for-green policy.