Adhering to the "red line" of 1800 million mu of arable land is China's arable land protection guideline and policy, and the "red line" places emphasis on both quantity and quality of arable land. Taking Shanxi's Anze County as an example, based on ecological safety and natural suitability criteria, we select 10 evaluation indicators to evaluate the farming suitability of existing land in the county. Results show that Anze County needs to reuse 48.7% of the existing arable land for ecological purpose in order to ensure ecological safety. It still retains 51.3% of existing arable land after abandoning tillage, which can ensure 0.15 ha of arable land per capita, 743.12 kg of grain per capita and 170% of food self-sufficiency rate, thereby fully ensuring food safety. The farming suitability evaluation of land resources should not only consider the natural suitability of land, but also consider ecological safety. Faced with the new situation of arable land protection, it is necessary to explore new farmland protection theories and indicator systems based on actual conditions, to meet the requirements of sustainable development of population, resources and ecology.