Abstract: Suburbanization is a stage of urbanization process. It means that population, jobs and service trades decentralize from the inner city to suburban area. It has greatly changed the economic and urban development in the developed countries Peter Hall’s model of urban change offered a framework which can easily identify whether a city is in the process of suburbanization. How about it in China as a developing country? When did it start? And what is the present situation in process? Beijing region can be divided into three levels:the inner city(cheng qu) ,the inner suburban districts(jin jiao qu) and the outer suburban districts and counties(yuan jiao qu xian). The author discusses the situation of Beijing from the data of three population censuses(1964,1982 and 1990) and considers that the suburbanization in Beijing has been in process since 1982. During 1982-1990, population of all districts of the inner city lost 82,000 people and in fact the permanent residents holding the household registration lost 144,000, about 6.12% of permenant residents in the inner city. Like the West, suburbanization in China also happened against the macro backgrounds of improvements of transportation and living conditions, growth of urban population moving from rural areas. But in the cast of the forces that make decentralization possible, China is different from the western countries. In China, the levels of economy and urbanization are rather low; the real middle class is not rich; only very few Chinese families own private cars; and the inner cities still have great attraction for Chinese people. Investigating the causes of decentralization, the author considers three points:(1) reform of urban land use system brings about migration from the core area.(2) Construction of a large number of city roads reinforces this process.(3) Reform of housing system and renovation of delapidated houses encourage outward movement. In a word, the large scale renovation of the old city has led to suburbanization in Beijing under the open door policy and the socialist market system. It wasn’t spontaneity of any individual but under the leadership of government and “Dan Wei” (work-units). Finally, the author puts forward some thought provoking and distinctive phenomena and problems that should be seriously treated.