The release of toxic and harmful gases seriously endangers human health and social and environmental safety. Sensitive determination of these gases is urgently needed to meet the demands of people and society. ZnO-based gas sensors have been widely used due to fast response, low detection limit, high selectivity, reliable performance and low manufacturing cost. In this review, we highlight the possible sensing mechanism of n-type ZnO materials, and discuss various strategies for enhancing sensitivity and selectivity of ZnO-based gas sensing materials, including regulation of the material morphology, composite of materials, photoexcitation, etc. Then, the current challenges of ZnO-based gas sensing materials are outlined, followed with the future research interests and directions of these materials. •This paper details the different gas sensing mechanisms of ZnO-based nanomaterials.•The relationship between the four different dimensional structures of ZnO and the gas-sensitive performance is explained.•The composite action of ZnO with other materials is described in detail.•We analyze the effects of visible light and ultraviolet light on the gas-sensitive properties of materials.