Abstract: For improvement of detection of a small static target in shallow water environments,a waveguide sonar processing scheme is proposed based on combination of MIMO(Multiple Input Multiple Output) and TRP(Time Reversal Processing).With a point target assumption,each element of a co-located transmit-receive vertical array time-reversal transmits one of orthogonal signals to illuminate a target in turn.And the whole array is used to receive target echoes.After all orthogonal signals are transmitted,a diversity algorithm is carried out over the received data to localize a target by matched filtering the replica of the steering vector for time reversal transmission.The time-division transmission strategy is to overcome the difficulty of separation of different target echoes at receiving end in conventional MIMO processing due to time-delay spread and Doppler spread of underwater acoustic channels.Echo-to-reverberation ratio is enhanced by physical time reversal transmission and numerical time reversal reception focusing resulting in suppressing reverberation.Numerical simulations and the waveguide tank experimental results have shown that the MIMO-TR processing can localize a target in a waveguide with a higher precision than the conventional active matched field processing.