Grains were originally called grains in ancient China, and later referred to food crops. There are many sayings about "five grains" in ancient times, and there are mainly two kinds. One refers to rice, millet, millet, wheat and rice; The other refers to hemp, millet, millet, wheat and glutinous rice. The difference between the two is that the former has rice without hemp, while the latter has hemp without rice. The ancient economic and cultural center was in the Yellow River valley, and the main rice producing area was in the south, while the rice planting in the north was limited, so there was no rice in the original "five grains".

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Although the concept of five grains has a history of more than two thousand years, the status of these crops in the national food supply has changed from time to time.

Millet, millet and other crops in the five grains have the characteristics of drought tolerance, barren tolerance and short growth period, so they occupy a particularly important position in the original cultivation of dry land in the north. In the Spring and Autumn Period and the Warring States Period, the characteristics of "keeping old is easy to do" were discovered, and together with millet, it became an indispensable food for people at that time. At the same time, it is found that lodging wheat (winter wheat) can be planted in late autumn and early spring, which can solve the problem of green and yellow. In addition, the invention of the stone mill at this time greatly improved the palatability of wheat from grain to pasta, which attracted widespread attention and developed into one of the main grain crops, comparable to millet. In the Confucian classic Spring and Autumn Annals, it is not a book, but if the crops fail, it is a book. It can be seen that saints attach the most importance to wheat and grains among grains. Agronomists Zhao Guo and Fan Sheng Zhi in the Western Han Dynasty devoted themselves to popularizing wheat planting in Guanzhong area.

The increase of Guanzhong population in Han Dynasty was closely related to the development of wheat planting. Until the Tang and Song Dynasties, the population in the north was more than that in the south. But after the Tang and Song Dynasties, the situation changed. The population growth of China is mainly concentrated in the southeast, that is, the land of Chu and Yue, which has been called "vast territory and sparsely populated" since Qin and Han Dynasties. In the Song Dynasty, the population of the south surpassed that of the north, estimated at 6: 4. Since then, the population density in the south is much higher than that in the north. The increase of population in southern China is closely related to rice production. Rice is very suitable for planting in the southern region with abundant rainfall, but at first it was inconspicuous and even excluded from grain. However, it came from behind.

After the Tang and Song Dynasties, the status of rice in the national grain supply was increasing. According to the estimation of Ming Dynasty and Song Dynasty, the grain supply at that time was mainly rice, while rice, wheat, millet and other grain crops accounted for only three tenths, which had been relegated to a secondary position. Soybean and hemp have withdrawn from the category of food crops and are only used as vegetables. However, when some crops withdrew from the ranks of food crops, some crops joined the ranks of food crops. At the end of the Ming Dynasty, corn, sweet potato and potato were introduced into China one after another, which became an important part of the main food crops in modern China.