Abstract: In response to the design constraints of railway enterprise's network architecture, physical isolation between the internal and external networks, this article proposes a video and audio security exchange technology for building the railway cloud video conferencing system. This technology enables the cloud video conferencing system to integrate railway enterprise's internal network and external network, as well as the Internet. The article focuses on describing the cross-network transmission mechanism and security guarantee system of the audio and video security exchange technology. Tests have shown that using this technology the railway cloud video conferencing system's video and audio data can be transmitted in a secure, efficient, and real-time manner between railway enterprise's internal and external networks, thus supporting simultaneous group meetings between the internal and external networks and meeting the application requirements of daily railway meetings and emergency command, providing key technical support for the digital transformation of railway.