Sulfur dioxide (SO₂) is a colorless toxic gas, and accurate monitoring of its concentration is important for safety. However, accuracy is often interfered by humidity. To address the issues, in this work, a self-calibrating SO₂ sensor based on CsPbBr/SnO was prepared, the sensor exhibited an excellent response to parts per billion (ppb) levels of SO₂ at room temperature, which is rarely achieved by other SO₂ sensors. The response sensitivity of the sensor to 600 ppb SO₂ reached up to 0.53 with response/recovery times of 17/285 s. In addition, the CsPbBr/SnO-based SO₂ gas sensor showed a low detection limit, good reproducibility, and high selectivity. Moreover, theoretical calculations show that the gas recognition mechanism is attributed to the significant changes in the band structure and density of states of the heterojunction materials CsPbBr/SnO after gas adsorption, thereby altering the charge carrier transport behavior and electrical properties. A self-calibrating algorithm MobileNetV2 was employed to eliminate humidity interference and effectively identify low-concentration SO₂ in humid environments, and the recognition accuracy rate is 0.85. This work demonstrates the production of a high-performance SO₂ gas sensor, and provides an effective method to eliminate the interference of humidity, making it significant in environmental monitoring and air quality control.