Man is a producer, who has created the great material civilization and spiritual civilization of mankind. At the same time, people are huge consumers, and the huge wealth it creates is for human consumption. People have their own reproductive characteristics, so population growth has a great impact on the geographical environment.

China is a country with a large population. In the long history, great changes have taken place in the population, but on the whole it has increased. As for the population figures before Qin and Han dynasties, it is difficult to be accurate because of insufficient data. Huangfu Mi, a native of A Jin, has the population figures from Dayu to the Warring States Period in his book "The Century of the Emperors", but it is hard to convince people, which may be a speculative figure, because people in the Han Dynasty are not clear about the previous population figures, and the population figures in the Jin Dynasty are hard to believe. According to the number of national armies during the Warring States Period, Mr. Fan Wenlan estimated that the population of the whole country was about 20 million at that time.

Since the Qin and Han Dynasties, all dynasties have attached great importance to population statistics and tried their best to find out the number of workers under their control. Because workers are basic social productive forces, they can create material wealth and are the main targets of exploitation by rulers. The number of military service and corvee is closely related to the population. Therefore, the population records after Qin and Han dynasties are quite rich. However, these figures are only official figures. In essence, people of past dynasties concealed population figures in order to escape corvee and taxes. For example, although we have made great efforts, there are still problems of underreporting and concealing population figures in cities, but the phenomenon of hiding household registration still exists in rural areas, especially in mountainous areas, because people have to apply for household registration, and those who do not conform to the family planning policy will be punished and fines will often occur.

Because the hidden population is a common phenomenon, the comparison of population figures in different dynasties can still reflect the increase or decrease of registered permanent residence and the size of population density. In addition to natural appreciation, death and natural disasters, the main factors affecting population growth and regional distribution in historical periods are political turmoil and war. At the same time, migration is also an important factor. Especially after the Western Jin Dynasty, due to the war in the north and the influence of its natural environment, a large number of people moved south, which reduced the population in the north and increased the population in the south.