Abstract: Previous studies about asymmetric acoustic transmission are limited to 2-D models,which can not be applied to the 3-D practical systems directly.To solve this problem,a 3-D pipe model that uses a built-in asymmetric geometry structure based on natural materials to achieve one-way acoustic transmission is studied.Due to the difference between the refractive indexes of the two natural gases (xenon and air) and the asymmetry of the structure,asymmetric acoustic transmission in the pipe is achieved,which means that when the incident acoustic waves transmit in one direction,they can reach the other side through the structure in the pipeline;while in the reversed direction,the acoustic energy is blocked by the structure.The results of theoretical calculation and simulation show that the asymmetric sound transmission effect of sound waves in 3-D rectangular waveguide is related to the thickness of the structure.That is,the thinner the thickness is,the broader the working band is.In addition,the designed waveguide features simple structure,transparent appearance,ultralight weight,etc.And it provides theoretical guidance for the design of new acoustic asymmetric transmission devices.