Abstract: When target is submerged into underwater acoustic waveguide, the modal coupling effects will be caused, thus leading to wavefield structure aberration. Investigation on the modal coupling response on vertical hydrophone array is benefit for detection of forward scattering under strong direct blast. The beamforming technology on vertical array is executed on the data from the forward scattering model and experiment respectively. The modal coupling response on the vertical hydrophone array caused by forward scattering from intruder is studied. The results show that the response aberration is significant when the intruder is close to receivers, and the arrivals will be expanded by the transformation from high order modes to low order modes. The field aberration could be acquired significantly with a narrow horizontal beam.