A high‐fluence reflection‐refraction x‐ray spectrometer allows spectral diagnosis of intense bursts ofxradiation from about 0.5 to 8 keV. Grazing‐incidence x rays, reflected first by a vitreous carbon mirror, are rereflected off the flat polished face of a plastic scintillator that is viewed by a photomultiplier tube. By making the scintillator‐mirror reflection angle greater than the carbon‐mirror angle, one efficiently refracts an energy band out of the incident spectrum into the scintillator. Reflection by the carbon mirror determines the high‐energy edge of the bin, whereas refraction into (or reflection from) the subsequent scintillator determines the lower edge. The current from the photomultiplier is a direct time‐dependent measure of the contents of the band. The sharpness of the band edges (about 0.1 keV) determines the narrowest measurable energy band and hence best possible energy resolution. The response to light of the scintillator‐photomultiplier limits the sensitivity. Measurements with continuum and monoenergetic sources are compared to theory.