A real-time double-beam in situ infrared spectrum system and a method thereof. The system comprises two identical infrared spectrometers and a double-beam infrared reactor cell, wherein the double-beam infrared reactor cell is formed by connecting a sample cell and a reference cell which are identical, the sample cell and the reference cell are at the same level and respectively correspond to a sample spectrometer and a reference spectrometer, the two infrared spectrometers are synchronously controlled by computers, to synchronously collect spectrograms of sample beams and background beams in real time, so as to obtain real information about a species on the catalyst surface changing with the reaction time, and eliminate gas molecule vibration spectrum interference in a real-time state and transmission spectrum interference generated under a heating condition. The present invention makes a characterization result become more accurate and reliable, so that real-time information about an active center of the catalyst surface, an active phase and an intermediate species at different temperatures may be obtained under a changeable gas phase component condition.