In order to improve the adaptive matching ability of quantum security network to data flow and improve network quality of service(QoS) and user experience, a software-defined quantum security network(SDQSN) based on Markov decision process(MDP) security policy is proposed. SDQSN can adaptively select different quantum key management strategies with the change of network traffic, and rely on the real-time monitoring of quantum link, calculate network revenue based on MDP, and determine the security policy of the system, so that the system can flexibly switch between the security policies of quantum encryption and classic encryption, and maintain network security and ensuring network QoS benefits. The simulation results show that the SDQSN is more flexible and dynamic adjustable than the traditional quantum security network, which can effectively ensure the overall benefits of the network and enhance the user experience.