Science comes from the needs of practice, which is the driving force to promote the development of demography and population studies. People have paid attention to population and its related problems for a long time. It has been more than 350 years since John Graunt published the book Natural and Political Observations Mentioned in a Following Index, and Made Upon the Bills of Mortality in 1662. Besides, it has been more than 130 years since demography was officially recognized as a discipline by the International Congress on Hygiene and Demography in Geneva in 1882. However, demography was not well developed before the Second World War. As the French demographer Alfred Sauvy described: “Demography has long been a weak science, either without teachers or students, but now it is gradually being paid attention to” (Sauvy 1982).