Based on the significant gradients and development differences of service industry development among mega cities in the Yangtze River Economic Belt，this report selects seven cities with a permanent population of more than 5 million in the Yangtze River Delta Region of the lower reaches of the Yangtze River Economic Belt as the comparative analysis objects，including Shanghai，Suzhou，Hangzhou，Ningbo，Nanjing，Wuxi and Changzhou. Compared with the important node cities in the middle reaches and upper reaches of the Yangtze River Economic Belt，the downstream megacities have obvious advantages in the scale and quality of service industry development. Compared with megacities with the same level and similar industrial structure，the characteristics will be more obvious in the aspects of comparability，directivity and regularity of development trend，and the guiding significance of policy level will be more prominent. Under the background of overall analysis，taking Nanjing as an example，through analyzing the change trend of leading industry scale and subdivision industry composition in Qinhuai District of Nanjing City，combing and summarizing the development experience and mode of megalopolis central urban area in recent years，the report forms a representative “Nanjing Qinhuai Sample” of service industry transformation in central urban area of megalopolis.