This article prepared GaN thin-film epitaxial wafers using the metal-organic chemical vapor deposition (MOCVD) technique, and further modified In2S3 using hydrothermal method. Combined with magnetron sputtering technology, a room-temperature NO2 gas sensor based on GaN/In2S3 was constructed. Using techniques such as scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the morphology, elemental composition, and chemical state of the materials were characterized. Gas sensitivity tests indicate that the sensor exhibits excellent response performance to 0.5×10-6–200×10-6 of NO2 at room temperature (25°C), with a theoretical detection limit of 11.34×10-9. The response/recovery time for 10×10-6 NO2 is 98/49 s, and it demonstrates good selectivity, repeatability, and long-term stability (response fluctuation < 3.2% over 3 weeks). Mechanism studies indicate that the synergistic effect of the In2S3 nanoflower structure and GaN enhances gas adsorption sites and electron transport efficiency, achieving high sensitivity detection through the redox reaction of surface chemisorbed oxygen and NO2. This study provides a new technical approach for the efficient detection of trace NO2 at room temperature.