The specimens with supplemental structural damping at both sides are frequently used in the measurement of viscoelastic material’s mechanics parameters through flexural resonating cantilever beam method（FRCBM）. Appropriate design of specimens decides the accuracy of experimental results. Though sensitivity analysis, influence coefficient was proposed and used in the analysis of experimental results which were affected by the measurement accuracy of thickness ratio, resonance frequency ratio, density ratio and loss factor of the specimen, and some significant technical specifications were proposed to help design the specimens. Finally, the applicability of the specimens damped both sides used in the measurement of mechanics parameters through FRCBM was analyzed.