Abstract: With the development of Internet and information technology, cyberspace, a virtual space, has appeared in the geographic research area in addition to a physical space, a physical space. In cyberspace, information can be produced, spread and received in almost one second, while such a process still rely on infrastructures in physical space. Due to that, some geographic phenomena may perform distinctively between cyberspace and physical space. Hence, there may be some new discoveries, both in theoretical and practical aspects, if differences between two spaces could be studied. From last century, there have been geographers who have studied the European and American cities networks through immigrants, traffic flows, goods flows and other indicators which can be measured in physical space. Until now, there are also some geographers putting their attention on cities networks in cyberspace, including Castells, Zook and so forth, whose researches inspire the paper a lot. Under such a background, the paper focus on cities network in Yangtze-River Delta, exploring the difference between cyberspace and physical space and causes behind it. The paper chooses two key issues in future development of Yangtze-River Delta cities (as The Planning of Yangtze-River Delta Region in The Period of 2010-2015 proposes) as the paper’s point cuts that are industrial development and regional innovation. With numbers of hyperlinks provided by search engines, Baidu and Google, the paper standardizes all the numbers first and then calculates the index of each city to measure its importance in cities network of cyberspace and compares the importance with the physical one (the physical importance will be quoted from The Planning of Yangtze-River Delta Region in The Period of 2010-2015). What is more, interaction between different cities in cyberspace will be measured in the paper as well and some compares are carried out on the basis of existing researches about Yangtze-River Delta cities network in physical space. After those, the paper finds that city’s networks in cyberspace are quite distinctive from the physical one. In cyberspace, some intermediate or even small cities treated in physical space play much important roles in networks while some large cities’ influence becomes inferior. Besides, the physical cities networks appear like hierarchies, but the networks in cyberspace not. Finally, the paper argues that city networks in cyberspace are still affected by basic geographical conditions, such as location, economic basis and infrastructure. And the distance between cities and information spreading also result in the difference between cyberspace and physical space. In the case, the paper makes the conclusion that city networks in cyberspace are the result of complex formation mechanism and cannot be determined by single factor.