Abstract: The rural development of China is undergoing transformation.The arable land is transforming from in support into limited.The peasant living is transforming from survival into comparatively well off.The economic institution is transforming from planning into market.The manner of land use is transforming from extensive into intensive.The rural and agriculture are transforming from exploitation into support by urbanization and industrialization.The relationship between rural and urban is transforming from difference into harmony.The agricultural economy is transforming from closed smallholder towards globalization.Therefore, demand for cropland will further increase, but the development of marginal arable land is limited.The shortage of cropland and the situation of food security will be further serious in the future.Among various factors threatening the sustainability of cropland, occupation on cropland by urbanization and industrialization is outstanding.This has made Chinese government and society heavyhearted.Therefore, the central government has paid great attention to cropland conservation and regarded it as a basic national policy.However, this basic national policy has not been implemented thoroughly in practice because the mechanisms of cropland conservation have not been established.The lower comparative benefit of agricultural land use is the major reason why cropland has continuously been occupied by urban development.Therefore the comparative benefit of agricultural land use must be raised in order to conserve cropland.The mechanisms of cropland conservation also include strengthening the role of government in cropland conservation, regulating land administrative behavior of government, identifying land administrative objects of government instead of market object, and implementing objects of government by means of land use planning in legislation manner.The development of urbanization and industrialization should be towards internal land development rather than external land expansion, and stress the intensive utilization of stock land in cities.