The invention discloses an air partial pressure measuring device, which relates to an air measuring device. The invention provides a measuring device which can stabilize environmental atmosphere, has high measuring accuracy, can be used to measure air partial pressure in high temperature environment simulation atmosphere, and in particular can measure the air partial pressure of controlling air flow quantity on line. An air preprocessing system and an air pressure measuring system are arranged on the invention. An oxygen delivering device, an argon delivering device, an air mixer, an air inlet pipe vertical lifting regulating device, and an aqueous vapor preprocessing device are arranged on the air preprocessing system, wherein the oxygen delivering device and the argon delivering device are connected through a triplet, the triplet is connected with the air mixer through an air pipe, the air mixer is connected with the aqueous vapor preprocessing device through the air pipe and the air inlet pipe vertical lifting regulating device. An oxygen measuring device, an aqueous vapor measuring device, and a high temperature environmental box are arranged in the air pressure measuring system, wherein the oxygen measuring device and the aqueous vapor measuring device are connected through an air insulating pipe and the triplet, and the aqueous vapor measuring device is connected with the high temperature environmental box through a sensor, a queous vapor chamber, and the air pipe.