Abstract: An energy spectrometer use to measured the intense γ-ray was developed and preliminary experimental results was obtained at rod pinch diode on inductive voltage adder (IVA). Si-PIN detectors array and Pb attenuator were used to design the energy spectrometer. The intensity of pulse γ-ray on IVA was measured by placing different thickness Pb plate in front of the energy spectrometer. Using the Monte-Carlo code, the energy deposition in sensitive region of Si-PIN detectors was calculated when the photons of different energies transmitted through the Pb plate. The sensitive curve of the detectors was obtained. Using correlation of theoretical quantity of electric charge and experimental waveform, the primal energy spectrum was calculated. The highest energy of the photons on IVA was 1.44