Abstract: The isolation and control of the vibration of structures under fixed rotating machineries is an important issue. While the vibration in vertical direction is extensively studied, the horizontal vibration is paid little attention. This paper investigates the dynamic behavior of a single-story frame structure under the action of a rotating machinery. The relation between the amplitude of the horizontal/vertical displacement and the natural frequency of the structure, the location and the operating frequency of the machinery is analyzed in detail. The results show that the amplitude of the horizontal vibration can be larger than that in the vertical direction under certain circumstances, which should be taken seriously in design.