With the development of networks and wideband technology, Next Generation Network (NGN) evolves into integrated transmission network of the multimedia information which including data, voice, image, the real-time tasks, etc. The traditional IP network provides only "best-effort" service and cannot meet the needs of multi-media applications and the different demands of a variety of users for network transmission quality. On the basis of a detailed analysis to Differentiated service (DiffServ) model and the characteristics of MPEG-4 encoding, the QoS control strategy of video streaming in NGN is proposed. That is a QoS control strategy which uses priority of Inter-Frame combining with DiffServ model in network congestion. Simulation and testing results show that the strategy can improve the transmission quality of the video stream effectively in the case of limited bandwidth.