The invention discloses a CO2 gas concentration monitoring device and method with the automatic temperature and air pressure compensation. The CO2 gas concentration can be accurately detected in a relatively wide temperature range and a relatively wide air pressure range, and the device and the method are applied to monitoring the CO2 gas concentration in a low-temperature low-pressure environment. The CO2 gas concentration is monitored by adopting a dual-wavelength infrared monitoring principle and a suction structure, and the device has the advantages of adaptation to a low-temperature low-pressure environment, high precision, high reliability and the like. The interference caused by factors such as light source instability is eliminated by adopting a dual-channel infrared detector, the absorption length of infrared light is increased by adopting a reflector, the environment suitability of the device is enhanced by adopting a heating element and a heat preservation material, the receiving light intensity is enhanced and the automatic temperature and air pressure compensation and correction is performed by adopting a conical optical collector, and the CO2 gas monitoring precision is effectively improved.