Network video technology develops quickly in recent years and the applications of network video are various. The effectively managing of the application based on network video is necessary for network flow management, network security, etc. and finding video stream from the network flow is the precondition and foundation. This paper analyzes the characteristics of the video stream packets, and draws a conclusion that each network video stream type can be labeled uniquely by one characteristic string, based on which, we can find video streams in network flow easily. The experiment results show that the method is able to find network video streams accurately.