Abstract: To investigate the application prospects and energy harvesting characteristics of two tandem cylinder with different diameter ratios in the field of wind vibration power generation,the vibration response and energy conversion characteristics of a two tandem cylinder system with different diameters are investigated under the condition of L/D=1.5,where the upstream cylinder is fixed and the downstream cylinder only vibrates in the transverse direction. The results indicate that the downstream cylinder exhibits both vortexinduced vibration and galloping vibration response,and the diameter ratio affects the vibration response and force characteristics of the downstream cylinder,which leads to the change of the lock-in velocity range. The galloping exhibits a harvesting power two times larger than the vortex-induced vibration. The energy conversion efficiency can be about 30% in the vortex-excited vibration region,but only10% in galloping region. Based on these analysis results,the advantage of d/D=0.8 energy conservation is more notable at low reduced velocity,but at high reduced velocity,the advantage of d/D=0.6 energy conservation become more significant.