中文摘要：

有别于探讨单个城市最优（绝对）规模的研究，本文从城市体系角度，运用Gibrat对数正态分布定律．以2011年为例．检验中国287个地级以上城市的实际规模与理论规模偏差，并划分出偏大、合理和偏小三种类型：偏大城市集中在300万以上人口规模的特大城市，偏小城市集中在人口规模100万左右的中等城市．而通常以绝对规模衡量的人口50万以下的小城市却相对合理。进一步地，构造居民效用最大化目标函数，分析市场机制下的集聚效应和政府引导下的公共服务对城市规模偏差的影响。多元Logistic回归结果表明：偏大城市由显著的集聚效应和优越的公共服务共同引致，其中，集聚效应通过提高生产效率、促进多样化就业和提升工资水平等途径推进城市规模过度增长，然而拥挤效应开始显现；相对偏小的中等城市尽管有一定的集聚效应，但滞后的教育、医疗等公共服务却制约了城市规模的合理增长。该结果间接表明，绝对规模小的城市因具有的公共服务功能超越了经济发展功能而相对合理。因此．中国城市体系优化的重点是加快发展具有一定集聚效应而公共服务相对滞后的中等城市。

英文摘要：

Different from the existing studies that focused on a single city＇s optimal size, this paper employs Gibrat＇s law of logarithm normal distribution to test deviations between the actual size and ideal size of 287 Chinese prefecture-level cities in 2011 from the perspective of cities＇ system, and correspondingly classifies them into relatively large, normal and small cities in terms of their positive, zero or negative deviation. In common sense, those cities with more than three million population are relatively large; Surprisingly, those medium-sized cities with average population of one million are relatively small while the 60 least cities with less than half a million population are relatively normal. By building a utility function of urban residents, we explain how the deviation is affected by agglomeration effects from market forces and public services from governments. Multiple logistic regression is used, and the results demonstrate that the large cities are relatively large, which is jointly caused by significant agglomeration effects and sufficient public services. As for the role of agglomeration effects, positive ones such as promoted production efficiency, varieties of employment and raised wage induce the large cities over-growing while negatively crowding effects help hold them to a reasonable level. The results also reveal that the medium-sized cities are relatively small, which is resulted from deficient public services such as educational and medical services despite being affected by weakly positive agglomeration effects at the same time. In addition, the results further imply that those small cities are reasonable for their responsibility of social services rather than economic growth. Therefore, the medium-sized cities should be paid more attention in order to optimize the Chinese system of cities, because they might own bright prospects based on agglomeration effects to a certain extent.