Abstract: In Z-pinch experiments on Primary Test Stand, a specially configured flat spectral response X-ray diode (FSR-XRD) was used to diagnose X-ray flux, which utilized a gold cathode XRD and a compounded gold filter to give rise to a nearly flat spectral response in photon energy range of 0.1-4 keV. To establish an absolute measurement of X-ray flux, each XRD and filter used was calibrated on beam lines 4B7B and 4B7A, Beijing synchrotron radiation facility. In typical experiments, uncertainty of X-ray power measurement inferred by FSR-XRD was 12%. In a single tungsten wire array Z-pinches experiment, diagnosed X-ray power exceeded 52 TW, energy was about 540 kJ. In dynamical hohlraum experiments, an FSR-XRD in the radial and an FSR-XRD in the axial were used to provide a time correlated measurement of X-ray pulse. In a typical dynamical hohlraum experiment, peak of axial X-ray power occurred before radial power by amount of about 1.2 ns.