The invention discloses a broadband acoustic coupler, and the acoustic coupler comprises a cylindrical housing. The center of the housing is provided with a cylinder, and the cylinder is connected with the housing through at least two screw blades with the gradually changing screw pitch, wherein the screw blades are distributed in a peripheral direction. The acoustic coupler is different from a horn-shaped waveguide structure which employs a material with the multi-layer impedance gradient changes or has the sectional area gradient changes. The acoustic coupler is very good in coupling effect for two types of waveguides with the impedance mismatching in a wide band range, and exerts no special requirements for the material of the structure, and just needs a condition that the material of the screw blades, the central cylinder and the external tubular housing is recognized as an acoustic material in the air. In addition, the coupler causes no pollution to the environment, and cannot cause any damage to the human body. The rigid structure facilitates the sustainable reuse. Because the couplers is wide in band, is environment-friendly, is rigid, is easy to integrate and is good in coupling effect, the coupler is very good in application prospect in the fields of acoustic energy converter design and acoustic imaging.