Population problem is an important part of human-land relationship, which is crucial in geography. As the world's largest nation with 1.3 billion people, China accumulated many historical statistical data about population distribution throughout history. Hu Huanyong designated the line from Heilongjiang Province to Yunnan Province as the population density boundary(Hu Line) of China in 1935. Population density, geographical structure, human lifestyle, and economic development significantly differ among different sides of Hu Line. To promote new-type urbanization, state leaders have considered whether or not the Hu Line can be broken and how to breakit.Basing from the proportion of definition by Hu Huanyong(3.87% and 96.13%) and Lorentz Curve Principle, this study characterized the Chinese population density boundary from 1935 to 2010.Boundary variations in recent 80 years were also analyzed. The first chapter of this thesis introduces the background and theoretical bases of the research. Then, a large number of population data collection and processing work were conducted. In addition, the methods and steps of accurate determination of population density boundary were described on the basis of Hu Line definition and Lorenz curve theory. Finally, changes in the boundary position and population proportion in each partition were studied. Since 1935, the population density boundary of China has migrated toward northwest. The observed migrations in Gansu and Ningxia provinces are the most dramatic, followed by those in Jilin, Inner Mongolia, Shanxi, Yunnan, and Southeast Sichuan. However, the boundary basically remains unchanged in the northeast Sichuan Province. In general, the population growth rate from 1935 to 2010 is higher on the northwest side of the population density boundary than on the southeast side. Hence, the population distribution in mainland China is unequal. The temporal and spatial distribution patterns of population in mainland China are revealed. Thus, this paper not only provides a scientific basis for the implementation of the urbanization strategy but also has practical significance to the implementation of national macro strategies.