The invention relates to a matching layer of an ultrasonic transducer. The matching layer comprises a low-density sound velocity layer and a high-density sound velocity arranged in sequence, wherein the low-density sound velocity layer is made of a material A, the high-density sound velocity layer is made of a material B, the low-density sound velocity layer is connected with a surface electrode of a piezoelectric material, and the high-density sound velocity layer is used for exposing to air or is connected with other devices. According to the technical scheme, the matching layer is made of asubstance capable of being obtained from the nature directly or indirectly, thickness of the matching layer can be controlled accurately by means of physical deposition, and the bottle neck in grinding of the thickness in the prior art is broken; as the thickness is controlled accurately, a matching system with an accurate acoustic impedance value can be obtained. Besides, the matching layer canbe applied to transducers having different special shapes, and the limit in conventional design can be broken through.