Abstract: In order to overcome multipath fading and eliminate intersymbol interference(ISI),a novel receiver algorithm for underwater acoustic coherent communication is proposed in this paper.The algorithm has two advantages.First,the algorithm combines adaptive decision feedback equalizer(DFE) and iterative decoding technology.Second,decoder adopts Turbo principle.The system can be regarded as a serially concatenated iterative decoding scheme whereby the inner decoder is substituted by the calculator of log-likelihood ratio(LLR),computational complexity is reduced.Simultaneously,adaptive decision feedback equalizer adopts the algorithm with variable step-size factor,so the speed ratio of the convergence is improved.Simulation is carried out to evaluate the composite algorithm performance.