Abstract: In order to explore the physical mechanism of an active triple-panel sound insulation structure and optimize passive sound insulation technique, it is necessary to firstly analyze the rule of sound energy transmission through the triple-panel structure. Firstly, the theoretical model of the panel-cavity-panel system is established using vibro-acoustic coupling approach. Then, the surface transfer impedance matrix of the incident and middle plates which radiate sound into enclosures is derived using numerical method. And the formulation of the radiated sound power of the two plates is also given. Finally the rule of sound energy transmission is obtained by analyzing the sound energy contained in each subsystem and the variation of radiated sound power of different types of mode groups in each plate. Results obtained demonstrate that, there exits four different sound energy transmission paths for four different types of mode group. Each transmission path shares the common characteristics, i.e., different energy transmission path has different pass-band in frequency domain. This is mainly due to the fact that the coupling strength of different coupled mode pairs of the panel and cavity is different.