Climate change remains as a major threat to food security, particularly for China because of its enormous population living off limited cropland. Evaluating the cost of climate change on agriculture requires estimates on both crop yields and cropland, where analysis on the latter has been limited. This paper utilizes unique high-resolution satellite data from 1980 to 2010 to estimate the effect of temperatures on cropland in China. We find that extremely high temperatures have significantly negative effects on the area of cropland. Our preferred specification suggests that an additional day with daily average temperature above 30 degree C in the past 10 years decreases the area of cropland by 0.81%, relative to the effect of temperatures between 10-20 degree C. We find that the majority of the decrease in cropland is likely to be the conversion to built-up lands. Under a “business-as-usual” scenario, climate change is likely to reduce croplands by 28.24%, or 500,000 km2, by the end of century. This will severely threaten the food security in China in the absence of countervailing investments.