Abstract: Cultivated land protection is one of the key difficulties in land management, and analysis on factors of cultivated land variation in China has significant meanings for development. Based on hypothesis that other factors are constant, conceptual model was firstly constructed for land use with integration of land assets, land use policies and land resources, then factors for variations of cultivated land in 1998-2002 were analyzed using econometric method on both national and regional scale, especially for the asset-political factors. The results show that, on a national scale, enhancement of land use policies, decrease of multiples of land value increment, increase of cultivated land inputs are helpful for cultivated land protection; increase of fertilizer leads to the decline of cultivated land; ratio of gross agricultural output, yields of crop and size of cultivated land per rural household do not explain the variations of cultivated land significantly. On regional scale, intensification of land use policies, promotion of supplement level for rural residents losing cultivated land and improvement of cultivated land input are advantageous for cultivated land protection. Specifically, reducing ratio of gross agricultural output in East China, and decreasing areas of irrigated land in West China, could be beneficial for maintenance of cultivated land. This paper concluded that integration of land resources-land assets-land use policies could better explain the variation of cultivated land protection, and then could take priorities to improve cultivated land protection in China based on the research results.