Traditional data center network has difficulty in guaranteeing the network bandwidth requirements of specified services. By developing network bandwidth guarantee services in Floodlight controller and designing client software using MVC (Model View Controller) pattern, the network bandwidth guarantee system based on SDN (Software Defined Network) is designed to enable users to monitor the network status real-timely and schedule the bandwidth guarantee strategies flexibly. Through the tests in the virtual network environment which is created by Mininet, the results show that this system can monitor the network status real-timely, schedule bandwidth guarantee strategies flexibly and then guarantee the bandwidth requirements for specified services in the network accurately and effectively.