Based on investigating and interpreting the characteristics of the size structure of regional urban system, this paper firstly aims to build a model on analyzing the relationships between reverse urban cumulative size and number of cities. Secondly, based on the sixth national population census data of 2010, traditional rank- size rule and the model of reverse cumulative size proposed in this paper are used to measure the inter-provincial differences and their spatial distribution characteristics of urban size structure in China. Thirdly, the geographic factors which have influence on regional urban system are discussed. The results show that the rank- size rule has few shortcomings in interpreting the characteristics of the size structure of regional urban system, especially for the urban system in which there is the distribution of primary city, two-centre city, or small number of cities. The shortcoming leads to the fact that there is no necessary linkage between the value of Q derived from the rank- size rule and the selected geographic variables. As a result, there are certain limitations in the comparative study between different regional urban system structures. Overall, the fitting provided by the model of reverse cumulative size given in this paper is better than that provided by the rank-size rule.Particularly, when the fitting provided by the rank- size rule is not ideal, the model of reverse cumulative size can overcome this shortcoming, and provides accurate fitting to more realistically and objectively reflect the characteristics of the size and structure of regional urban system. Moreover, the results also show that there is a close statistical relationship between the selected regional variables, such as regional economy, urbanization, population density and the composite index, and the value of β given by the model of reverse cumulative size. In the process of urbanization, path of the urban system coordinated with regional development should be explored in term of the tendency of development and characteristics of different regions. According to the statistics derived from the general regression model and spatial auto regression model, there is a weak spatial linkage between the formation and evolution of the regional urban systems of each province in China. That is to say, the formation and evolution of the regional urban systems of each province is in a close state of isolated development. The reason should be related to the strict administration and policies of household registration and the prevalence of local protectionism in China.