Abstract: In this paper, the design of large-dimension rectangular horns consisted of twosections was studied, the cross section of one section keeps constant,the other varies according to the law of exponential, conical and catenoidal curves. By introducing. the apparent elasticity constants, we analyzed the coupled vibration of this kind of horns, denyed out the frequency equation. The measured results of the, resonant frequency of horns show that the calculated results of frequency by coupled vibration theory are neater to the measured ones than those by one-dimentioal vibration theory.