Abstract: A* Orthogonal Matching Pursuit(A*OMP),a pseudo greedy algorithm that can improve performance of OMP,is applied to the underwater acoustic channel estimation.Furthermore,by optimizing the initialization procedure and applying different criterion of stopping iteration in order to avoid unknown errors,we proposed a modified A*OMP channel estimation method.Simulation and sea trial based on an Orthogonal Frequency Division Multiplexing(OFDM)OFDM system are carried out to test the performance.And the influence of the pilot interval is not obvious on performance of modified A*OMP.The numerical simulation shows that the error of proposed algorithm is lower by 2 and 1 orders of magnitude respectively compared to OMP and A*OMP.The results show that the proposed method outperforms the OMP and traditional A*OMP algorithm in the estimation accuracy and the communication output bit error rate,and reduces the bit error rate by about 42.0%and 4.7%respectively.