Through a simple solution method, TiO(Acac)₂ was used to in-situ coat the all-inorganic perovskite material CsPbBr₃. After heating at 400 ℃, CsPbBr₃@TiO₂ core-shell structure microcrystals were directly prepared. The crystal structure, microscopic morphology, and chemical composition of CsPbBr₃@TiO₂ microcrystals were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). It was confirmed that the in-situ metal oxide coating on the perovskite formed well-dispersed spherical shell structures with sizes of 4 ～ 8 μm. A CsPbBr₃@TiO₂ thin film gas sensor was constructed on a fluorine-doped tin oxide (FTO) electrode using spin-coating method. The sensitivity of the sensor to H₂S gas was tested at room temperature. The results show that the sensor has a detection limit of 25 ppb (1 ppb=10^-9) for H₂S gas, with a response and recovery time of 24/21 s to 100 ppb H₂S, and a sensitivity of 0.59. The response curve exhibits good cyclic stability. Moreover, the sensor maintains over 90% stability within 30 d of exposure in air and possesses excellent gas selectivity and humidity resistance. Photoluminescence (PL) spectroscopy, time-resolved photoluminescence (TRPL) spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis), and ultraviolet photoelectron spectroscopy (UPS) were employed to analyze the band positions, charge dynamics, and coordination mechanisms. The sensing mechanism was elucidated using the oxygen adsorption principle. This work provides a new approach for the stable monitoring of low concentrations of H₂S gas at room temperature.