Abstract: In this paper,vibrational power flow and the mechanism of structure-borne noise transmission in the complex flexible coupled system of machinery mounted on multi——storey plant buildings are systematically studied from the viewpoint of power flow.In view of practical isolation designs in engineering,an asymmetric isolation system with multiple mountings on a flexible foundation is modelled,in which the dynamic interactions between machine and floor,and among different mounting points are taken into account.In addition,the transmission characteristics of the structure-borne noise of the system concerned are analysed with the use of substructure mobility synthetic technique.Furthermore,the power flow spectra of the present system are calculated and compared with those of totally symmetric system under various parametric conditions to reveal the effects of asymmetricity on power flow of isolation systems.Finally,new approaches to the control of structuresborne noise for this kind of problems are proposed.