The invention relates to a nuclear resonance fluorescence-based pulse gamma ray energy spectrum measuring system and method. The device comprises lead collimators, a HPGe detector and a specific target sheet; the lead collimators and the specific target sheet are sequentially disposed in the beam direction of pulse gamma rays to be measured; the HPGe detector is located to one side of the pulse gamma rays to be measured; and an included angle between the HPGe detector and the beam direction ranges from 90 degrees to 120 degrees; a plurality of target materials are stacked so as to form the specific target sheet; and the energy level of each target material is within the energy range of the pulse gamma rays to be measured. The method includes the following steps that: 1) a HPGe detector isadopted to detect the number R of photons emitted by the pulse gamma rays to be measured during nuclear resonance fluorescence; 2) photon density is calculated; and 3) and Gaussian fitting is performed on the basis of the photon density, so that the energy spectrum distribution diagram of the pulse gamma rays to be measured is obtained. With the method of the invention adopted, a pulse gamma ray energy spectrum measurement experiment is simple to set, later-stage calculation is simple, and measurement accuracy is high.