Abstract: Key technologies of underground wireless video monitoring system were researched and implemented including video data acquisition, coding and decoding, network transmission, etc. The system codes video data by use of MPEG-4 protocol, transmits the coded data through WiFi network and RTP stream medium protocol, and decodes and displays received video data by use of monitoring host. The experimental result showed that the system could transmit 25 frame of MEPG-4 video data and the video images are clear and fluent.