Device and method for measuring in-situ time-resolved X-ray absorption spectrum. The device comprises an X-ray source, a first slit, an acousto-optic tunable X-ray filter, a radio frequency transmitter, a second slit, a front ionization chamber, a front ionization chamber signal amplifier, a sample to be tested, a rear ionization chamber, a rear ionization chamber signal amplifier, a data collector, and a computer. The X-ray source, the acousto-optic tunable X-ray filter, and the radio frequency transmitter are used to generate a monochromatic X-ray beam; the front ionization chamber is used to measure the intensity of the X-ray beam before passing through the sample; the rear ionization chamber is used to measure the intensity of the X-ray beam after passing through the sample; the front ionization chamber signal amplifier, the rear ionization chamber signal amplifier, the data collector, and the computer are used for data acquisition and data processing.