Abstract: Study on high-density city is meaningful for practical issues since cities in the world were growing more and more high-density. Based on statistical data of 1513 cities with more than 500,000 population in year 2012 by Demographia, standard and global distribution of high-density cities were studied, the results indicate: Firstly, the standard of high-density city should be about 15,000 person per square kilometer, higher than this level city show “high-density” features which include land use, street and building, and transportation. Secondly, high-density cities are mainly distributed in developing countries which charaterized with lower industrialization, lower urbanization and larger population. Thirdly, high-density causes of developed country and developing country are different, as developed country is mainly caused by re-urbanization and developing country mainly by urbanization. Finally, several suggestions for further studies were given which include residential model, traffic management, resource distribution, public health, green space and so on.