Tuned mass damper (TMD) as a kind of passive vibration reduction device, has widely used in engineering structures. Howerver, the damping effect of traditional TMD would decrease dramatically even there is only a small change of the main structure's dynamic characteristics. As a new kind of smart material, the stiffness of magnetorheological (MRE) would change with the change of magnetic field applied. So we can change the stiffness of MRE to adjust the natural frequency of TMD. Based on this idea, we have proposed a new kind of frequency adjustable TMD based on MRE. While the magnetorheological effect and the deformation of MRE are mutually restricted, the allowable small deformation of MRE cannot meet the actual substantially deformation of TMD. In this paper, the deformation of MRE is enlarged by the gear disk which greatly increases the amplitude of the frequency adjustable TMD based on MRE, and then the mechanical model of this new device is deduced. on the basis of this, the natural frequencies of the main structures are identified by the combination of the Hilbert-Huang Transform (HEIT) and the Random Decrement Technique (RDT). A better damping effect can be achieved by changing the external magneitci field of this new kind of TMD to track the natural frequencies of the main structure. Lastly, a pedestrian brige is used as the engineering background and the simulation of vibration control use frequency adjustable TMD is calculated. The results show that, compared to traditional TMD the damping effect of this frequency adjustable TMD is hardly affected by the change of main structure's natural frequency. There are a wider vibration frequency, a more stable damping effect and a better deformation capacity of this frequency adjustable TMD.