Since the entrance to 21st century, the growing popularuty of mobile communication devices such as smart phones and PDAs, as well as the fast development of wireless communication technologies such as 3g wireless network and GPS, the mobile information network has become the new trend of informatization. On this new trend, residents are able to access Internet information anytime anywhere; and thus promote the penetration of ICTs into almost every aspect of people's daily life. With the development and applicaton of LAD, LBS and other related technologies, residents' activity and their real-time geospatial information has been recorded. These big "traces" with geospatial information should be emphasized for geographers' analyses which will undoubtedly provide support for the construction of "Smart city". With a soring popularity of online social network as Sina micro-blog (the most influential social networking platform in China) and the LBS checking-in application, this paper tries to visulize the characteristics of urban activity space in Nanjing, using these LBS checking-in data in Nanjing city from Sina micro-blog. The results indicate obvious hierarchical cluster and strip layout along transport corrider, with a somewhat tiny spatial difference between female's and male's. Compared with the urban hierarchy based on urban populaion, The urban activity space shows a consistency with the urban hierarchy based on urban population, but with a more apprent pramid structure in which the gap between differnent level is larger.