The development and application of network and communication technology has made school teaching manifold, and learning activity through network has become an important medium for human beings to acquire knowledge. Modern distance learning combines computer, communication and multimedia technology to provide interactive environment between students and far-away teachers. In recent years, advanced countries in Europe and America devoted great efforts to distance-learning research and aimed at applying the technology to different areas of education and training to improve the deficiency of manpower and instrument in distant region. Currently, the distance-learning projects proceeded in our country are real-time group broadcasting, course on demand, and virtual classroom. Among them, real-time group broadcasting and course on demand belong to synchronous and asynchronous video-teaching systems respectively, and virtual classroom is a member of network-learning management systems. We will focus on the study of a synchronous video-teaching technology. Asynchronous video-teaching systems utilize video-on-demand (VOD) technology to download video-teaching programs from video server through network. Although such systems can not satisfy the requirement of real-time interactivity, they provide all-time distance-learning service and students can proceed the learning and manipulation according to their learning speeds. Most VOD systems adopt client-server structure, so video programs can be transmitted from far side to the screen of personal Computers by using plug-in software. Some systems even provide real-time broadcasting and schedule functions. In this paper, we will study asynchronous video-teaching technology, including the structure of VOD systems, the method to develop video-teaching program, video file compression technique, and the effect of network bandwidth on the performance of video-teaching systems.