In this paper,the acoustic functions of the melon of the Chinese river dolphin(Lipotes vexillifer)are studied.Based on the comparison between the directivity patterns of the whole head and the skull,it is suggested that the melon plays an important role in beamforming.At the frequencuy of 40 kHz,the—3 dB beamwidth of the emitted vertical beam of the whole head is approximately 21.6°,withthe major axis elevated 10°above the ristrum plane;the—3 dB beamwidth of the horizontal beam ofthe whole head is approximately 20°,with the major axis deviated 12°rightward from the body axis.The vertical and horizontal—3dB beamwidths of the whole head are 9.4°and 13°,narrower than thoseof the skull respectively,and the directions of the major axes are different for both cases.It canbe seen that the melon narrows the width of the main beam and greatly reduces the side lobes of thebeam formed by the skull.The distribution of the sound velocity in the melon tissue is measured andthe distribution pattern is drawn.Fr In this paper, the acoustic functions of the melon of the Chinese river dolphin (Lipotes vexillifer) were studied. Based on the comparison between the directivity patterns of the whole head and the skull, it is suggested that the melon plays an important role in beamforming .At the frequencuy of 40 kHz, the-3 dB beamwidth of the emitted vertical beam of the whole head is approximately 21.6 °, with the major axis elevated 10 ° above the ristrum plane; the-3 dB beamwidth of the horizontal beam of the whole head is approximately 20 ° with the major axis deviated 12 ° rightward from the body axis. Vertical and horizontal-3dB beamwidths of the whole head are 9.4 ° and 13 ° narrower than those of the skull respectively, and the directions of the major axes are different for both cases. It canbe seen that the melon narrows the width of the main beam and greatly reduces the side lobes of the beam formed by the skull. The distribution of the sound velocity in the melon tissue is measured and the distributi on pattern is drawn. Fr