With the rapid growth of cloud applications and users, Data Center Network (DCN) has become a critical component in the cloud ecosystem to sustain remarkable computation demand. It is facing great challenges in performance guarantee, security enforcement, and resource and energy management. Software Defined Networking (SDN), as an efficient way to collect network information and perform network management, has been adopted in DCN to enable automated network configuration and management. In this paper we aim at surveying the state-of-the-art techniques of using SDN in DCN and discuss the way SDN help DCN. We first present the introduction of SDN and DCN, then survey the SDN based DCN, and finally show some lessons and future trend.