The invention provides an air sounding type water vapor detection device and method, wherein the device comprises a refrigeration and heating control module, an infrared light emission receiving module, a four-channel alternating current excitation resistance measurement module, a sensor, a pulse wide modulating and driving circuit module and a digital signal controller. According to the invention, by the steady and reliable digital technology low in cost, an original method which is based on absolute reflected light detection and has high accurate amplitude measurement requirement is converted to be a technology based on active infrared reflected light change rate detection, strict shielding requirement on ambient light is not needed any more, the instrument structure is greatly simplified, cost is greatly lowered, detection performance is greatly improved, and meanwhile, the user is more convenient.