Abstract: In order to solve the problem of accurate measurement for high-energy γ ray, a set of three-crystal electron-pair spectrometer was developed based on the self-developed scintillation crystal detector. The double-escape peak energy spectrum above 1.5 MeV γ ray of ⁵⁶Co source was measured. The three-crystal electron-pair spectrometer can effectively reduce the ratio of peak to continuous background compared with LaBr₃ detector. It lays the technical foundation for accurate measurement of high-energy γ ray from nuclear resonance reaction (p,γ) and laser Compton scattering (LCS).