Abstract: With the development of cloud computing technology and the promotion of the new infrastructure strategy, data centers are acting as the linkage between digital & information networks and traditional industries. In the context of energy Internet, exploring internal operation flexibility of data centers is an important research field to accomplish the deep integration of data network and energy network, and thus boost system flexibility. On the basis of relevant literature hitherto, the potential and significance of collaborative optimization between data center and power system were analyzed in detail in this series of articles. In this first paper, the basic characteristics and spatio-temporal scheduling flexibility of two types of workloads in data center were analyzed based on the actual operation situation. The data center energy consumption models explored in existing literature were classified into two types. On this basis, the potential flexibility, including temporal flexibility, spatial flexibility and multi-energy conversion flexibility of data centers, was further analyzed. In addition, the trend of energy management in data centers was inferred and explained considering relevant policies at present.