Since the Reform and Opening up, the regional development gaps have become increasingly prominent with the rapid development of China’s economy and society. The gaps among the East, Center and West have been widely concerned, but the gaps between the South and North are less concerned. Under the background of the new era, the gaps between the South and North have become the prominent issues affecting the sustainable development of China’s region, and reflected the evolution trend of overall pattern of land space development and utilization. This study used the regional gravity center model to analyze the changes pattern in the population and economic gravity centers, and used the geographic detector model to measure the impact of economic and social factors on population density and economic growth. Several key conclusions were reached. 1) The population gravity centers generally moved southwest, with the movement divided into three stages: moving southwest rapidly (1978–1999), moving southeast (1999–2010), moving southwest (2010–2018). 2) The economic gravity centers generally moved southwest, with the movement divided into four stages: moving northwest (1978–1991), moving southeast rapidly (1991–2003), moving northwest slightly (2003–2012), moving southwest rapidly (2012–2018). 3) The development gaps of population and economy between the South and North were becoming increasingly salient in China, and require more attention from government and academia. 4) The order of factors influencing China’s population density is: urbanization > traffic convenience > external development > market prosperity > science and technology > industrialization > policy support. 5) The order of factors influencing China’s economic growth is: industrialization > market prosperity > science and technology > policy support > external development > traffic convenience > urbanization.