The change of urban commercial area is one of the most important study topics of urban economic geography. With the development of a city, the old city is no longer the only area that works as commercial and business districts. The loss of uniqueness of the old city will lead to a series of changes of the commerce in the old city, including the changes of commercial space. This paper takes a north-south line from Jishuitan to Xuanwumen in the old city of Beijing as a survey transect, makes field investigation and orders the historical data, and try to find the trend of the hierarchical structure changes of commercial space in the old city of Beijing in the decade between 1996 and 2006, and finds that some specialized commercial centers appear at the same time. This study uses the Central Place Theory, the concepts of Flexible Specialization and the Central City Evolution Theory as the main theories for the analysis of the reasons of commercial space succession, and takes transact research and the method of landscape records as the main methods of data acquiring. Apart from borrowing methods from other researchers, this paper tries to use the index of "function number" for measuring the grade of commercial areas, and use the index of "lineal density" for measuring the degree of specialization of commercial areas. Two months fieldwork helps giving the location of each enterprise in statistic data exactly, and explores to make up for the defect of data from historical document. The conclusions of this paper are: 1) the succession of commercial space in the old city of Beijing can be analyzed from the change of the coverage of commercial centers. In the decade between 1996 and 2006, the coverage of the second grade of commercial centers gets smaller; some seriate specialized commercial centers emerges; 2) the main reason of the change of the central place pattern and the coverage decrease of the second grade of commercial centers is the transportation development of the north-south traffic line; 3) spatial flexible specialization motivates the appearance of specialized commercial centers in the survey transect. The urban expansion expands the difference between the type of commerce in the central city and on the periphery; the competition between the new commercial forms at the urban edge and in the old city gets intensive. Therefore the specialized commercial areas with luxury goods draw close to the high-grade commercial center. The appearance of specialized commercial centers is also in conformance with the need of the upgrade of the central place functions. Two shortcomings of this paper are: 1) only the shops and stores along the north-south street are concerned, and that near the crosses are not concerned, which are along the east-west streets; 2) because of the lack of the commercial enterprises distribution in the whole city of Beijing, only the hierarchical change in the transect can be described, and the conclusion now can not infer the succession in other parts of the old city.