Abstract: Nuclear resonance fluorescence(NRF) experiments can be used to study the low excitation energy levels of photonuclear reactions. Shanghai Laser Electron Gamma Source(SLEGS) designed and constructed a NRF spectrometer consisting of two large-scale coaxial high-purity germanium(HPGe, \phi 80 mm×70 mm) detectors and two CLOVER HPGe(4×\phi 50 mm×70 mm), the large-scale HPGe detectors obtained relative efficiency greater than 100% and energy resolution better than 0.3%@1 332 keV. The spectrometer adopts Mesytec MDPP-16 digital pulse processor and MVME acquisition system, which can read and record the amplitude and time information of the HPGe preamplifier output signal. The Add-back mode and Reduction mode of the CLOVER HPGe detector are studied. Results show that Add-back reconstruction can significantly improve the full-energy peak efficiency and peak-to-total ratio, the full-energy peak efficiency after Add-back reconstruction can be improved by more than 21% at 1 460 keV energy. The detector energy resolution is slightly degraded due to the coupling between multiple crystals introduced by the Add-back reconstruction. Whereas at reduction mode, it can reduce the compton peak, improve the peak-to-total ratio, and maintain the energy resolution as good as the Direct mode, however, a certain amount of full energy peak efficiency is lost.