Abstract: Since the 1990s,China has been entering into a hyper-growth period,and urbanization in China is developing rapidly.Many large cities in China are also undergoing significant population growth and thus their spatial structures have been changed a lot. Previous studies showed that a few large cities had stepped into suburbanization process.For example,development in cities of Shanghai,Beijing and Guangzhou tends to form a polycentric pattern.However,case studies of other Chinese large cities have not been unfolded yet.It is very worth to explore more Chinese large cities for geographical scholars with the perspectives of population growth and spatial structure evolution.Based on existing theory and analysis method,this paper takes Nanjing city as a case study.The paper firstly analyzes the population spatial expansion process in Nanjing city by using geographical analysis methods,including street zoning method and circle division method.Then it simulates the polycentric development of urban population distribution through statistical models.The results show that:along with the total population growth,Nanjing's high population density areas have extended to inner suburban areas,forming a circled spatial expanding approach,which is the result of natural urban population growth.At the same time,the population densities of district-governments'seats and prioritized development areas in outer suburban areas also become very high,forming a fog-jumping spatial expanding approach.Population growth in these places has a close relationship with the government regulations and policies.The government-led population growth in urban China is different from that in edge city,suburban magnetic center and rural secondary employment center in the Western countries.Moreover,we also find that population spatial distribution in Nanjing has also been experiencing a tendency of polycentric development.Except the downtown area,Shanxi Road Street has become a population growth center,and the Wanda Plaza of Hexi New City Zone is becoming another population growth hot spot as well.This paper makes a good foundation forward to summarizing population spatial evolution theory in Chinese large city.Besides,it also provides some important experiential evidences for levels of government on optimization and regulation of Nanjing city's population distribution.

Key words: large city, population distribution, spatial expansion, polycentric development, Nanjing