Based on the new round of 100 billion catty of grain production capacity increase action, this paper uses the growth accounting framework to reveal the sources of China’s rice, wheat, and corn production capacity increase. Results show that: total factor productivity improvement is the main source of grain production capacity increase for rice and wheat, and its contribution for the two grain reaches 85.39% and 100.93%, pulling the production capacity increase of them by 0.91% and 2.39% respectively. For corn, before the 18th National Congress of the Communist Party of China, land is the main source of its production capacity increase, with a contribution rate of 64.13%, pulling corn production capacity up by 4.11%. Since the 18th National Congress of the Communist Party of China, total factor productivity has shifted to be the main source of production capacity increase, with a contribution rate of 64.38%, pulling corn production capacity increase by 1.27%. This paper provides important references for the optimization of grain structure as well as the sustainable growth of grain production.