Software-defined network is based on flexible and open standards,which manages network functions and services by the control layer.And it has the unique advantages of control-separation and centralized control.The moving target defense technology is dedicated to build an ever-changing environment to increase the uncertainty of the network system,which requires a flexible and customizable,centralized and controllable network architecture to implement it.Therefore,the combination of moving target defense and software-defined network have become a more valuable research hotspot.Firstly,the basic concepts of software-defined network and moving target defense were introduced,the security threats of software-defined network was summarized,and the realization model of moving target defense for SDN network was described.Secondly,the technical methods for moving target defense were summarized respectively form the data layer,control layer and application layer of the SDN.Finally,summing up the challenges of existing SDN dynamic defense,and looking forward to the development direction of moving target defense technologies for the SDN.