Well-defined polyhedral Cu2O exposing different crystal facets are synthesized via a facile solution-phase method, and the facet-dependent gas sensing properties are investigated. The results show that cubic Cu2O exposing (100) facets has higher sensitivity to NO2, acetone and benzene than octahedral Cu2O with (111) facets. More importantly, the cubic Cu2O has high selectivity to NO2 and acetone at varied working temperatures by different sensing mechanisms of adsorption, chemical reaction, and intrinsic carrier excitation, as verified by the catalytic and electric property measurements. The higher sensitivity and selectivity of cubic Cu2O is explained by the relatively lower work function of (100) surfaces than that of (111), which induces a thicker surface hole accumulation layer and thus, a higher bulk hole activation energy (0.55eV and 0.36eV respectively). The synergistic effect of catalytic and electric properties gives rise to gas sensitivity decrease with the reduced percentage of (111) facets, which is beneficial to the gas sensing material design and also, is promising for the future highly sensitive and selective gas sensor fabrication.