Due to the wide coverage of the Wide Area Network (WAN), the single-controller deployment of Software Defined-Wide Area Network (SD-WAN) cannot meet its needs in capacity, load and security, the deployment of multiple controllers becomes necessary. However, the static configuration of the whole network after the deployment of multiple controllers was difficult to be adapted to the change of dynamic network flow, which can easily lead to load unbalance of controllers, reducing the network performance. To solve this problem, a multi-controller deployment algorithm named SC-cSNN (Spectral Clustering-closeness of the Shared Nearest Neighbors) was proposed to reduce the propagation delay between the controller and the switch, and a dynamic switch migration method based on features such as time-delay, capacity and security was proposed to solve the problem of controller overload. Simulation results indicate that compared with existing controller deployment algorithms based on k-means and spectral clustering, the multi-controller deployment algorithm and the dynamic switch migration method can effectively minimize the average maximum delay between the controller and the switch and solve the problem of controller overload.