Abstract: Under the dynamical load, the interaction between thestructure and its interior equipment is evident.In this interacting system, the structure is considered as the main-structure,and the interior equipment is regarded as a sub-structure. Its mechanism andinfluencing factor of reducing vibration are studied by means of frequencydomain analysis. The result of study indicates that the mechanism isthat the sub-structure provides an inertial dynamic load, and the loadcan reduce the vibration of the interacting system.