Today, the world is witnessing an enormous new economic wave, which has become an important and growing contributor to economic development. However, few studies compare the overall development of all new economic sectors in different cities or countries. Therefore, the purpose of this study is to contribute to the literature on the 21st century new economy in China, which is viewed as a crucial development direction. Accordingly, the new economic situation in 2018 in 15 major cities of China is evaluated by constructing an index system and adopting some new big-data technologies, whereby a new economy comprehensive index (NECI) for each city is obtained. This study finds that the cities ranked from high to low in the NECI are Beijing, Shanghai, Shenzhen, Guangzhou, Hangzhou, Wuhan, Chengdu, Nanjing, Chongqing, Suzhou, Zhengzhou, Wuxi, Tianjin, Qingdao, and Xi’an. Among them, Beijing, Shanghai, and Shenzhen belong to the first hierarchy. The findings provide a nuanced perspective on the intercity comparison of the new economy, and the index system presented in the study is urgently-needed for policy makers. Finally, based on the case study of Chengdu the study offers rich insights to city administrators in terms of how to promote the new economy.