For two species influence factors of the effective electromechanical coupling coefficient (k2eff) , i.e., the electrode/piezoelectric layer thickness ratio of FBAR and caxis orientation of piezoelectric layer, a simulation model of threelayers composites FBAR was established focusing on the variable thickness ratio and variable degree of caxis orientation in this paper. By using a FBAR with a resonant frequency of 2.185 GHz as a case study, it′s simulation results showed that the k2eff  declined slightly when thickness ratio was 0.206, but the thickness of Mo electrodes was 0.247 μm and AlN piezoelectric layer was 1.119 7 μm, which resulted in good electrical properties of FBAR and reduced the process complexity and fabrication time. On the other hand, when the caxis inclination angle was 30, it would reduce the k2eff of FBAR. A the same time, the impedance characteristics curve of FBAR would present a strong sense of spurious resonance, causing the lateral energy leakage in FBAR and deteriorating the insertion loss of FBAR filters. So the key process parameters should be strictly adjusted to fabricate the high quality AlN thin film. In addition,the appropriate relaxation of the resonant frequency increment of FBAR would enable the k2eff  to have a certain redundancy, which could compensate the k2eff  reduction resulted by the preparation process.