At present, most cities in China are in rapid expansion by constructing new urban districts. At the same time, the traffic problem becomes more and more serious. From the viewpoint of system theory, this paper proposes the basic concept of the coordinated development of the traffic between central cities and new urban districts, analy- zes the basic requirements of the coordinated development in the aspects of technical coordination, benefit coordina- tion, system coordination and function coordination, and builds up two evaluation index systems to respectively de- scribe the internal and the external coordinated transport sub-systems. Moreover, an evaluation model correspon- ding to the basic concept and the evaluation index systems is constructed to evaluate the coordinated development of traffic between a central city and its new urban districts. Finally, by using the traffic between Xi＇an and Gaoling, which is found primarily coordinated but trends to grow, as an example, the correctness of the proposed theory and methods is verified.