Cultivated land is the cornerstone of national food security. However, there have been debates about how much cultivated land should be preserved to meet the bottom line of China’s food demand in the new era. Therefore, this study started from clarifying the minimum demand of cultivated land under different scenarios. A prediction model was constructed, which considered population, grain consumption per capita, and grain yield per unit cultivated area. Then, the cultivated land demand was simulated under three scenarios completely self-sufficient, highly self-sufficient, and moderately self-sufficient. Combining with the prediction of the cultivated land change, cultivated land protection was proposed at three levels, including the ideal amount that could be protected (IACP), the basic amount that should be protected (BASP), and the minimum amount that must be protected (MAMP). The results show that: in 2020, 2025, 2030, and 2035, the IACP requires to preserve at least 1.920 billion, 1.839 billion, 1.847 billion and 1.657 billion mu, respectively; the BASP requires to preserve at least 1.849 billion, 1.772 billion, 1.778 billion and 1.612 billion mu, respectively; the MAMP requires to preserve at least 1.780 billion, 1.709 billion, 1.709 billion and 1.551 billion mu, respectively. There into, the BASP of cultivated land may be chosen as a rational strategy of protection. However, if the strict control policy is abandoned in the future, it will be difficult to meet the demand of completely self-sufficient in grain production in 2030 and 2035. Therefore, differentiated,continuous and strict policy of land protection should be implemented to ensure food security in China.