Abstract: To develop low-cost NO₂ gas sensors with excellent sensitivity, SnS₂/rGO two-dimensional (2D) heterostructure composites were successfully constructed in this work using polyethylene glycol 400 (PEG400) as a morphology-controlling agent and dispersant, and graphene oxide (GO) with different contents as precursors, via a hydrothermal method involving in situ reduction of GO and its simultaneous combination with SnS₂ nanosheets. The results indicate that the introduction of rGO effectively suppressed the agglomeration of SnS₂ nanosheets, increasing the specific surface area of the composite from 18.89 m²/g to 32.37 m²/g; XPS and HRTEM analyses confirmed the formation of a heterojunction at the SnS₂/rGO interface. Gas-sensing performance tests showed that the SnS₂/2G composite achieved a response of 15.4 toward 1 × 10⁻⁶ NO₂ at 100℃, approximately three times that of pristine SnS₂. Its response and recovery times were 62 s and 88 s, respectively, with the recovery time shortened by about 86% compared with pristine SnS₂, and it also exhibited good humidity resistance, selectivity, and long-term stability. DFT calculations reveal that the adsorption energy of SnS₂/rGO toward NO₂ (−0.217 eV) is about 2.2 times that of pure SnS₂ (−0.099 eV). Mechanism analysis suggests that the built-in electric field at the p-n heterojunction interface promotes charge transfer, while rGO serves as a high-mobility electron transport channel that optimizes carrier transport, synergistically enhancing the gas-sensing response. This work provides a new idea for designing NO₂ gas sensors with two-dimensional heterojunction structures.