Abstract: To solve the problem of continuous phase rotation of the equalizer output during the process of channel equalization,a fractionally-spaced super-exponential iteration（FSSEI） algorithm with second order digital phase-locked loop（DPLL2） is proposed.The proposed algorithm realizes the transmitted sequence recovery by utilizing FSSEI algorithm to restrain the multi-path effect and using DPLL2 to eliminate continuous phase rotation of the equalizer output.The results of tank experiments show that the proposed algorithm has faster convergence speed and lower residual mean square error than several other blind equalization algorithms.It can solve the problem of continuous phase rotation and reduce bit error rate of underwater communication systems.