To perfect the simulation model of a piezoelectric unimorph cantilever and to design optimal piezoelectric vibrators, the analysis model of equivalent viscous damping coefficient for the vibrator was established according to the mechanical vibration theory and damping theory. Then, the influences of the material properties, structural dimensions as well as the cross-section shapes on the machinery and electricity damping coefficients were analyzed. Finally, three groups piezoelectric vibrator samples with different shapes and sizes were prepared , and the impact vibration test were performed to verify the theoretical analysis. The results show that the impact of piezoelectric material layer on the overall damping depends on the elastic modulus ratio of the substrate and the piezoelectric material. In each vibration cycle, the piezoelectric material power loss is proportional to the cube of the cantilever length and inversely proportional to the width. However, the damping ratio to determine an amplitude amplification factor is not varies with the structure size monotonically. The difference beween the experimental results and theoretical model is 2.5%-14.7%,which proves the reliability of the theoretical model. Moreover, the piezoelectric unimorph cantilever with optimal static characteristics may not have the best dynamic characteristics under the same extreme load. These results can offer reference for the optimal design of piezoelectric vibrators.