Abstract: The thirty years of reform and opening are thirty years for China cities’ quick development, during which many problems appeared such as the disorder of city space, inequality and deterioration of internal and external environment, and so on. Compacted city theory was advanced by European scholars to resolve such problems as city decline, city expansion as well as limiting factors of land resources, which mainly involves theoretical ideas of high density city exploitation, mixed land use, decentralized convergence, prior development of public transportation and constructing harmonious city condition. This article analysed and generalizes the definition and characters of compacted city, summarized the synthethical measurement methods, and put forwards the advantages and disadvantages both of the single index measurement and multi-index measurement. From the basic concept of compact city, the paper discussed the measuring way for city compactness. It is of great guiding significance for theory and practice for improving intensive degree of Chinese city space utilization, avoiding disorder spread of space and promoting the sustainable development of urban to grasp the developing current situation of compact city and to establish an effective pushing model for compact city.The paper believed that compact city includes the compact of city form, the compact of function and the compact of population. The core connotation of that means a high definition state of city and is a strategic mode of efficient and high quality of urban development.Based on the related theories about core meaning of compact city both at home and abroad, the paper constructs the appraisal index system of the synthesis level of the city compactness embarking economic compactness, land compactness, traffic compactness and population compactness. With the method of entropy, the paper researched the comprehensive city compactness of 13 central cities of Jiangsu Province. and finds out that all the city compactness of the cities are low, and the spatial discrepancy of compactness is obvious. At the same time, the article also classified city compactness into three grades: compact, less compact and non-compact. On the basis, the article drew the conclusion that the impetus of city compactness involved the system forces, the market forces,population forces, the traffic guide forces and nature forces. The multiple linear regression models show that system forces, market forces and population forces promote the city compactness obviously. But the traffic guide forces should be improved rapidly.