Abstract: Suprathermal electron is an important factor influencing ignition in inertial confine fusion. Measuring results of hard X-ray spectrum could get suprathermal electron temperature and suprathermal electron quantities. This project mainly built a system to measure hard X-ray spectrum in energy region of 5 keV to 88 keV utilizing filter-fluorescer method. The system accurately calibrated its scintillators sensitivity with an uncertainty of less than 10%. System signal-to-noise ratio was increased by shielding the interference from system insides and environment of measurement. System output linearity was enhanced from 4 to 104 by replacing a photo-multiple-tube which could stand bigger current and changing the size of aperture or filters thickness. Finally, the system succeeded in measuring a precise hard X-ray spectrum of Au-plane target in SG-Ⅲ prototype.