Abstract: Based on GIS spatial model and combination of land use data, urban planning data and farmland grading data, the potential urban sprawling and the risk to cultivated lands in Hangzhou Bay area were analyzed. Results revealed that the study area was characterized by high quality and density cultivated lands, whereas the construction lands would expand 9.4×104 hm2 in this area from 2005 to 2020. Therefore, cultivated lands would decrease 7.1×104 hm2, which was the main source of new construction lands occupying 75% according to present urban planning. Cultivated lands with high quality would decrease largely and rapidly. In the total decreased area, cultivated lands ranking from 1 to 5 according to farmland grading were 67.5%, and those ranking 1 and 2 would decease 37.16% and 35.52% respectively from 2005 to 2020. Suggestions include that a quality assessment of the occupied cultivated lands is carried out with farmland grading, and urban planning is adjusted to reduce the impact of construction on cultivated lands to safeguard the ability of food production.