A low-loss dual-band bandpass filter (BPF) for millimeter wave based on dual-mode groove gap waveguide (GGW) is proposed in this work. Dual-mode resonators including TE102 mode and TE201 mode are utilized to form dual-band response. Two vertically stacked GGW cavities are properly coupled by a cross-shaped coupling aperture. Additionally, the resonant frequency of TE201 mode can be controlled by adjusting the position of two pairs of perturbed pins, realizing an adjustable passband. For verification, a second-order dual-band GGW filter operated at 25.2 and 26.99 GHz is designed and simulated, and the minimum insertion losses (ILs) of two passbands are 0.18 dB and 0.24 dB, respectively.