In recent years, with the rapid development of cloud computing and extensive application of virtualization, the composition, structure, function, scale and application mode of data center network are profound changing. Thorough analysis of its characteristics is the basic research on modern data center network and is of important significance. It can help us to understand its work mechanism, improve its performance, and reasonably design its resource management scheme and system. However, comprehensive analysis and research on the characteristics of data center network is still lack. In this paper, we study a couple of basic characteristics of modern data center network from several important aspects, including structures, application properties, flow characteristics and virtualization features. Some preliminary conclusions of each aspect are obtained: for modern data center network, its mainly constructed based on commodity Ethernet switches and its application mode is changing from monopolization or physical isolation mode to cloud computing, and its flow exhibits locality and dynamic. To support the migration of virtual machine, data center network should be a two-layer network. In the last, influences of these characteristics on network resource management are further studied, which are also the important research directions in the future. We hope these studies can offer a useful support to the theory study and system design.