The work aims to study the influence of vibration motor excitation on the unloading of unloading device under full load, and optimize the vibration characteristics of the unloading device. The unloading device was modeled by SolidWorks, and the natural frequencies and modal shapes of the first 8 orders were analyzed by Ansys Workbench software to find the weak structure area. Taking the weak area of the unloading device as reference, the installation position of the vibration motor was optimized by comparing and analyzing whether the external excitation frequency and the natural frequency of the unloading device resonated. The modal analysis showed that the seventh order natural frequency of the unloading device was in the resonance region, which might lead to the resonance of the unloading device. Integrated with the harmonic response analysis, the amplitude displacement near the natural frequency of the first, fourth and fifth orders of the unloading device was the largest and the maximum amplitude displacement of the response component of the unloading device was 1.8, 1.86 and 1.9 mm when the vibration motor was respectively installed at E, F and G. Through comprehensive analysis, it is concluded that 16 Hz and 33 Hz should be avoided when the external excitation frequency is applied on the unloading device, and the vibration source installed at F could be optimal. This can provide the necessary basis for the unloading device in the actual design and manufacturing process.