In　this　work,　the　mechanism　of　the　effect　of　the　surface　state　of　tin　oxide　on　its　reductive　gas　sensitivity　was　investigated.　A　simple　strategy　was　used　to　synthesize　tin　oxide　samples　with　various　structures.　The　strategy　involved　a　hydrothermal　reaction　and　calcination　to　transform　the　triclinic　Sn3O4　structure　to　the　tetragonal　SnO2　structure.　A　combination　of　experimental　and　theoretical　results,　was　used　to　investigate　the　reasons　for　the　good　reductive　gas　sensitivity　of　SnO2　compared　with　those　of　other　tin　oxides.　The　results　show　that　the　origin　of　the　gas　sensitivity　is　surface　bonding　states　that　arise　because　of　unoccupied　electron　orbitals.　In　contrast,　for　Sn3O4,　there　are　surface　antibonding　states　of　the　terminal　Sn　atoms　with　lone　pairs　and　gas　adsorption　is　difficult.　The　effect　of　the　surface　state　on　the　gas　sensitivity　is　also　related　to　the　electronegativity　of　the　atoms　on　the　adsorptive　surface,　and　the　electronic　interactions　between　a　gas　molecule　and　the　adsorptive　surface.　The　results　provide　a　feasible　strategy　for　enhancing　the　gas　sensitivity　of　metallic　oxides　by　modulation　of　the　surface　states　of　the　metal　oxide.