Abstract: When discharge faults occur in dry air switchgear, the air decomposes to produce diverse gases, with NO₂ reaching the highest levels. Detecting the NO₂ level can reflect the operation status of the equipment. This paper proposes to combine ZnO cluster with MoS₂ to improve the gas-sensitive properties of the monolayer. Based on the Density Functional Theory (DFT), the effect of (ZnO)_n size on the behavior of MoS₂ is considered. Key parameters such as adsorption energy and band gap of (ZnO)_n-MoS₂/NO₂ system were calculated. The ZnO-MoS₂ heterojunction was successfully synthesized by a hydrothermal method. The gas sensor exhibits a remarkable response and a fast response-recovery time to 100 ppm NO₂. In addition, it demonstrates excellent selectivity, long-term stability and a low detection limit. This work confirms the potential of the ZnO-MoS₂ composite structure as a highly effective gas sensor for NO₂ detection, which provides valuable theoretical and experimental insights for fault detection in dry air switchgear.