This paper proposes a third-order dual-bandpass filter based on vertically integrated metal sheet waveguide(MSW) for FR3-Band applications. The filter adopts a nine-layer vertically stacked structure, and realizes dual-band passband response by exciting the TM11 and TM12 dual-mode resonances. Through the rational design of resonant cavities, coupling slots and transition matching structures, the inter-cavity coupling strength and external coupling matching performance are precisely controlled, thus ensuring optimal dual-band frequency characteristics and filtering performance. Simulated results show that the filter has dual passbands with center frequencies of 15.4 GHz and 18.0 GHz, and the corresponding 3-dB fractional bandwidths are 6.22% and 4.61%, respectively.