The article focuses on the research of a reliable data transmission extension protocol -- UDT based on UDP, the related implementation method and transmission control method of multimedia data real-time and reliable transmission, the improvement to algorithm of its related methods in specific applications; as well as the improvement to AIMD (Additive Increase and Multiplicative Decrease) congestion controlling algorithm, proposing DAIMD congestion controlling algorithm; the sending rate increment is changed from the constant quantity to the variable quantity which continuously reduces with the continuous increase of the sending rates, so it not only makes a more rational use of limited network bandwidth, also reduces the larger oscillation in the network data transmission; the improvement of validation mechanisms, propose validation mechanisms based on the combination of time and data packets numbers, and improve the efficiency of data transmission. When the multimedia data network transmits, the transmitter and receiver need to identify a network transmission protocol. According to the above analysis, UDP is a simple transmission level protocol, non-connection-oriented, and itself does not provide data retransmission and confirmation, therefore adopting UDP as the network transmission protocol can improve the data transmission efficiency, besides UDP supports the webcast function, suitable for multimedia data network transmission . However, the characteristic of multimedia data network transmission requests the network transmission protocol can handle the phenomenon of delay and vibration in the transmission process; can handle bursting multimedia data transmission; can judge the network condition according to the reception quality of the receiver and the sender can make the appropriate response; can ensure the reliability of multimedia data network transmission and so on. Features of UDP its own design make it deal with such situations not very well, also UDP limits the sending data packet size each time; when the multimedia data network transmits, a video data often exceed this limit. Therefore, according to the previous analysis of multimedia data network transmission characteristics and technical requirements, this article studies the reliable data transmission extension protocol -- UDT based on UDP, and improves the related algorithm and control mechanism in the protocol to make it more suitable for the multimedia data network transmission in the embedded video surveillance system.