Low bit rate speech coding of 2.4kbps is actualized by mixed excitation linear prediction algorithm, which meets the requirement of high data rate of underwater speech communication system and the limit of high communication rate of underwater acoustic communication technique. In the process of speech coding, a great deal of speech data is compressed to high speed underwater acoustic communication, and the main characteristics of speaker are remained perfectly. Meanwhile, the anti-interference ability is improved obviously by the speech based on contact conduction microphone as input signal. This underwater speech coding technique and differential OFDM technique are combined and experimented in the communication distance of 393m, 1310m and 2000m in the lake. The real-time transmission of speech signal is presented in the condition of complicated multi-path in the extremely shallow sea. The results show the synthesized speech has well quality of intelligibility and clarity, which satisfies the demand of un...