It is important to accelerate the reasonable adjustment of planting structure to stabilize the market supply and demand of feed grains, and promote the high-quality development of livestock industry. Based on the feed grain and livestock data from 2000 to 2020, a partial equilibrium model was constructed to predict the future trends of feed grain and livestock breeding and to simulate the impact of the adjustment policies of the planting structure, such as"grain to feed"crop conversion, on the demand and supply of feed grains and livestock. The results show that: (1) Under normal conditions, the supply and demand of China' s feed grains will continue to increase; however, feed grain yields exhibit a declining trend. The supply of domestic feed grain needs to be supplemented by imports. By 2025, China' s feed grain supply is expected to reach 336 million tons, of which domestic output, imports, and exports will account for 209 million, 127 million, and 231 thousand tons, respectively; the scale of livestock breeding is expected to reach 4.25 billion sheep units. The demand for feed grains is expected to reach 306 million tons, and the price of feed grains is expected to rise to RMB 3.04 yuan/kg. (2) The implementation of the"grain to feed"policy is still feasible. Furthermore, the promotion effect of the continuous reduction of the acreage of feed grains on the growth of the scale of livestock breeding is more significant than that of expanding the acreage of feed grains. The implementation of the"grain to feed"policy has decreased the output of feed grain, an effect that has contributed to the continuous expansion of the livestock breeding scale, resulting in the growth of feed grain imports while increasing the price of feed grain. If the"grain to feed"policy aims to increase the livestock breeding scale, it would be more appropriate to maintain a relatively large reduction area during the 14th Five-Year Plan period. However, increasing the support for planting grain and forage maize could be considered. The research results can provide support for the design of planting structure adjustment programs and consolidate the foundation of feed grain and forage safety for livestock breeding.