Abstract: An underwater acoustic channel is a complicated medium for data communications,especially in shallow coastal regions,which is important in military and commercial applications.Signals sent through a shallow water channel are often corrupted by inter-symbol interference(ISI) and intra-symbol interference,seriously affecting the underwater acoustic communication quality.We propose an adaptive equalization algorithm based on the decision feedback structure,and using a fractional sampling method.The performance is compared with the baud-spaced adaptive equaliz-ation in computer simulations.Quadrature phase shift keying(QPSK) signaling is employed to make efficient use of the available bandwidth.Mont Carlo simulations are performed,showing that the proposed algorithm with high convergence rate and low steady state error results in improved communication effectiveness and reliability.