Associated with population and income growth, grain consumption in China is expected to increase, and thus has inevitably influenced the food security. Using statistical data of the Food and Agricultural Organization of the United Nations (FAO) from 1978 to 2017, this study adopting the vector auto-regression (VAR) model and implied demand approach, projected the future consumption of major grains (rice, wheat, maize, and soybean) for food, feed, and other uses in China during 2018–2030. On this basis, it further discussed their implications on grain security. The results showed that during 2018–2030, the Chinese dietary structure would continue to shift from food grain to animal foods. As a result, the grain’s food consumption will decrease slightly (1.5%), while the feed consumption will increase significantly (31.4%), contributing 71.4% to the total increase of grain consumption. By 2030, the total grain consumption will increase by 20.2% to 846.2 million tons, of which 50.2% will be consumed for feeding animals. In the total consumption, maize will be the largest consumed grain variety, accounting for 39.2%. The security of rice and wheat would be optimistic in the future, while the security of maize and soybeans is likely to decline, and thus needs to be given high priority. These findings have great policy implications for improving the grain security, suggesting that in addition to promote the expansion of maize and soybean growing area by adjusting the cropping structure of the arable land, great efforts should be paid to improve the yield of both crops. In addition, residents should be guided to adjust the dietary structure, and also, it is important to improve the animal feeding efficiency.