Abstract: The horizontal ground movement correlates to its vertical movement and, therefore, the vertical earthquake action will exert an influence on the damping effect the magnetorhrological damper (MRD) is available to obtain. The structure of MRD under the action of earthquake in both horizontal and vertical direction is studied theoretically with a kinematic differential equation given to analyze how the vertical action affects the structure of MRD. The results show that MRD has a good controllable effect whether the vertical action of earthquake is considered or not. However, the seismic responses from MRD structure increase differently with the vertical of earthquake, i.e., the greater the vertical action, the higher the increment. It is thus highly recommended that the influence of vertical earthquake action on various MRD structures shall be taken into account in high-intensity earthquake regions.