To analyze the causes of the fluctuation in relative humidity at the ABSL?2 laboratory and propose countermeasures. According to the ABSL?2 laboratory humidification, dehumidification, air humidity, automatic control, sensor working principle. Owing to inconsistency of the air supply in various laboratory areas, humidified steam is not continuously supplied, and excessive dehumidification time and humidity sensor monitoring error occur, resulting in the fluctuation of relative humidity. The influences of these factors were analyzed one by one to establish an effective method of humidity stabilization. Through real?time regulation of air valves, continuous and stable steam supply, establishment of a two?level surface cooler, regular maintenance and updating of humidity sensors, and appropriate management practices, we further improved the stability of the relative humidity index of the ABSL?2 laboratory. Improve the level of laboratory biosafety, and provide information for the future design and management of air?conditioning systems in laboratory animal centers.