Abstract: The UWA (Underwater Acoustic) channel is probably one of the most complicated environments for data communication. Three structures of high speed UWA communication systems are designed. And performance is compared through the systemic simulations. A UWA channel model including the time-varying fading, multipath and additive noise is built. All of the three schemes use the phase-coherent QPSK modulation techniques. Spatio-temporal processing combined space diversity and adaptive equalizer (with DPLL embedded) is used in the receiver. There are three forward error correct coding schemes: convolutional codes, serial concatenated code (convolutional code + RS code), parallel concatenated code (Turbo code). The performance of the systems using the different number of the water acoustic receivers to achieve diversity is studied. And the performance of the systems utilizing three coding schemes is studied.