A flexible and dynamic videoconferencing system (FDVCS) is developed. The system aims to reduce the burden of the users under the operational environment with insufficient computational resources, such as the Internet environment with small-scale computers at homes and offices, by embedding flexibility to the conventional videoconferencing system. Moreover, FDVCS enables any more people to see and hear each other in real time. In other words, the point number of the system can be increased or decreased dynamically. The result of the experiments shows that the design is reasonable for construction of FDVCS. The system design involves many things such as the design of the hardware, the system software, and the application software, etc. This paper emphasizes on the design of the application software called MCU (multipoint control unit), the design of the system control module, the design of the audio multipoint processor module, and the design of the video multipoint processor module, in such a system.