A novel bulk acoustic wave (BAW) resonator structure with air edge reflectors is proposed. The air reflectors provided at the border of the resonator suppress the acoustic wave leakage travelling in lateral direction. The difference of acoustic impedance at the air edge interface is so large that the reflectivity is almost unity which indicates perfect reflection. As a result of optimized lateral structure, the Q-factor at antiresonance frequency (Qa) is improved significantly to 2740. Furthermore, the effective electro-mechanical coupling coefficient (kt 2) which is essential to achieve wide band-width of RF filters is increased considerably by 14%. We also perform multi-physics simulation and investigate the effect of the lateral wave leakage for the BAW structures.