Abstract: Taking prefecture cities of Chinese mainland as examples, and changing the model of urban flows into the model of urban extrovert service function, this paper quantifies freight extrovert service function of central cities based on different transport models with the aid of ArcGIS.The comparison of the calculation of related data in 1989 and 2008 reveals a spatial distribution law and a hierarchical structure of freight extrovert service function of central cities, with which the position and function of each city in the national and astride regional freight spatial connection is investigated.The results are shown as follows. First, the freight extrovert service function of central cities in China is distributed widely in north and intensively in south, and the advantage of urban agglomeration is obvious. Second, the proportion of the extrovert service value distinctly decreased in eastern coastal provinces in recent 20 years, while that of freight increased, which indicates that the mass freight had a larger proportion in the country.Third, there are significant differences in the extrovert service pattern of central cities'freight based on different transportation modes.As a result, different central cities formed the function division in the different spatial transportation connection.Fourth, this research divides the freight extrovert service ability of central cities into four functional levels, which are the national, the astride regional, the provincial and the civic.
As a conclusion, the freight extrovert service function of central cities has been affected by various factors in China.It is directly proportional to urban GDP and freight scale, and it is greatly affected by economic location and transportation location.Also it has a close relationship with the structure and distance of different types of freight transportation.

Key words: central city, freight extrovert service function, hierarchical structure, spatial system