A novel X-ray tube spectrum reconstruction method has been proposed based on transmission measurements. Aluminum bars of varying lengths attenuate the X-rays to different levels. The detectors are of lutetium yttrium oxyorthosilicate scintillator and silicon photomultiplier. With the detected X-ray intensities, the X-ray spectrum is unfolded using the least square method. The detectors, aluminum bars, and collimating apertures are integrated in a detection module made of lead. Its response to X-ray is calculated by Monte Carlo codes Geant4. Due to the high photon flux, the detectors work in current mode.The electronics system, consisting of 24-bit high-precision ADCs with 144 KSPS sampling rate and field programmable gate array, makes the data acquisition process effective and precise. Measurements on a 70-k Vp tungsten anode X-ray were taken to verify the method. The unfolded spectrum agrees well with the simulated spectrum,demonstrating that the method is reliable and practical. A novel X-ray tube spectrum reconstruction method has been proposed based on transmission measurements. Aluminum bars of varying lengths attenuate the X-rays to different levels. The detectors are lutetium yttrium oxyorthosilicate scintillator and silicon photomultiplier. With the detected X-ray intensities The detectors, aluminum bars, and collimating apertures are integrated in a detection module made of lead. Its response to X-ray is calculated by Monte Carlo codes Geant4. Due to the high photon flux, the detectors work in current mode. electronics system, consisting of 24-bit high-precision ADCs with 144 KSPS sampling rate and field programmable gate array, makes the data acquisition process effective and precise. Measurements on a 70-k The unfolded spectrum agrees well with the simulated spectrum, demonstrating that the method is reliable and practical.