In this paper, a design method for obtaining an ultra-wideband thin film bulk acoustic resonator (FBAR) filters based on aluminum nitride thin film with a relative bandwidth of about 70.61% has been proposed, that is a bandwidth of 4.835 GHz at a center frequency of 6.5 GHz. The simulation result shows that by series-parallel inductance and series-parallel capacitance at the inductance end, the influence of harmonic resonance point interference caused by adding external inductance on the bandpass can be eliminated, realizing the ultra-wideband of FBAR filters. This work opens up a new way to design ultra-wideband bulk acoustic wave filters with bandwidths exceeding 3 GHz.