Abstract: Ocean ambient noise mainly includes uncorrelated noise and correlated noise, and the uncorrelated noise only affects the diagonal elements in the covariance matrix. A high array gain beamforming with diagonal reducing is presented ultilizing this feature. Firstly, the constrained value is selected by some criterions, and the array weight norm constraint is used to ensure the robustness of this method. Secondly, the diagonal reducing value is calculated by the newton iteration method. Finally, the covariance matrix which subtracts the diagonal reducing value is used in the MVDR beamformer. Both the numerical simulations and experimental results show that the proposed method can increase the array gain and the resolution capacity of multi-target. This method can provide compromise between array gain and robustness by changing the diagonal reducing value.