From the 80s, with the rapid development of the Internet, videoconferencing made significant progress and played an important role in economics, education and remote healthcare. A lot of applications and models appeared. More and more companies and people get used to communicate through a video conferencing service. Therefore, it is important to measure and analyze their quality and performance for the researchers who want to develop new applications. In this thesis, we made a survey about the existing Desktop video conferencing applications on the Internet, and then picked four typical video conferencing applications as experiment objects. We investigated the mechanisms of the application, their traffic characteristics and their communications structures. Through global experiments, we analyzed the different aspects of Quality of Experience (QoE) for these applications. Audio quality, video quality, interactivity level, audio/video synchronization and worst cases are studied. The measurement results help us to understand the behavior and mechanism of video conferencing, and also the QoE of different applications.