Fe-doped graphyne (Fe-GY) is a promising 2D carbon platform for chemiresistive gas sensing because transition-metal dopants can introduce chemically active sites while the conjugated carbon network provides an efficient charge-transport channel. Herein, density functional theory calculations were performed to elucidate the adsorption selectivity and electronic-response mechanism of Fe-GY toward three representative volatile organic compounds (VOCs), namely formaldehyde (HCHO), acetone (CH3COCH3), and benzene. The computed adsorption energies indicate strong binding for oxygenated VOCs (HCHO: -1.35 eV; acetone: -0.95 eV) and moderate binding for benzene (-0.53 eV), while typical background gases exhibit weak or unfavorable adsorption (O2: -0.13 eV; CO2: -0.06 eV; N2: +0.19 eV). Charge analysis reveals pronounced interfacial charge redistribution for HCHO and acetone, whereas benzene shows negligible charge transfer, consistent with distinct interaction natures. Electronic-structure calculations further demonstrate that adsorption induces substantial band-structure modulation: the nearly gapless Fe-GY substrate (0.007 eV) develops an opened gap upon adsorption (0.192, 0.362, and 0.392 eV for HCHO, acetone, and benzene, respectively), accompanied by characteristic band signatures. Together with PDOS, charge density difference and IGMH analyses, these results provide a coherent mechanistic picture linking adsorption energetics, orbital hybridization, and electronic response, highlighting Fe-GY as a viable sensing material for VOCs, particularly oxygenated species.