In this study, thickness vibration mode piezoelectric devices for AE sensor application were simulated using ATILA FEM program, and then fabricated. Trajectory resonant displacement and electro mechanical coupling factors of the piezoelectric devices were investigated. The simulation results showed that excellent displacement and electro mechanical coupling factor was obtained when the ratio of diameter/thickness($Phi/T$) was 0.75. The piezoelectric device of $Phi/T$=0.75 exhibited the optimum values of fr= 183 kHz, displacement= $4.44{ imes}10^{-7}[m]$, $k_{33}$= 0.69, which were suitable for the application of AE sensor piezoelectric device.