Abstract: Soft X-ray Dante spectrometer is one of the primary instruments to diagnose the X-ray radiation emitted by Z-pinch plasma. To obtain the spectra and power of X-rays, unfolding treatment of the measuring data is a must. The structure of a recently developed eight-channel Dante spectrometer is introduced and a smooth unfolding algorithm using parabolic B-splines is presented. Numerical simulation shows that, for blackbody spectra with temperature ranging from 20 to 250 eV, both the spectra and power are accurately recovered. Experimental waveforms measured during Z-pinch experiments performed on the Yang accelerator. The 40.5 GW X-ray peaking power and 851 J X-ray energy unfolded from the measurements of the Dante spectrometer were in agreement with the corrected results of the sofe X-ray po