Abstract: Vibration transmission is an important part of vibration theory and an important criterion for evaluating vibration control effects. For positive and negative isolation of discrete structures, the transfer rate is clearly defined. Since the vibration of the elastic structure is not only transmitted through one point, it is necessary to discuss how to define the transverse vibration transmission of the elastic structure. Through the elastic beams supported by springs at both ends, three kinds of transmissibility definitions for the positive isolation of the transverse bending vibration of the elastic structure are given, which are the transmissibility of the component forces of the two support ends and the transmissibility of the combined force of the two support points. The results show that the transmissions defined by the three methods may be equal or there may be large differences. More complex than the discrete structure vibration isolation theory. In order to promote the development of basic theories and applications of vibration mechanics, it is recommended that this basic vibration problem be included in the textbook as part of the course on vibration mechanics.