For the access control problem of media distribution network in software-defined network (SDN) environment, an access control scheme considering the optimization of service node and transmission link service performance is proposed. The scheme utilizes the SDN controller's direct control over the router and the perception of the entire network, and jointly optimizes the service performance of the service node on the application layer and the service performance of the transmission link between the service node and the user on the network layer, reducing the impact of link congestion on data transmission and user service quality. Firstly, a partial observable Markov decision process (POMDP) model is established for the access control process of the SDN service system; Then, the observation-based random strategy is used as the access control strategy of the system; Finally, the access control strategy is optimized by the policy gradient algorithm, solve out the optimal strategy of the model. The simulation results show that compared with the best-effort service strategy, the optimal access control strategy based on POMDP model improves the system performance by 10%, and verifies the effectiveness of the proposed method.