A key diagnostic for absolute radiation flux and radiation temperature in hohlraum experiments is the Dante soft x-ray spectrometer in which grazing incidence x-ray mirrors are used to diminish the high energy response of the filters. The reflectivities of planar mirrors made of different materials were calibrated in BSRF in 2009.Considering both the influence of the source such as the spectra resolution,harmonic and the attenuation of the source intensity and the influence of the coherence of two detectors responses,we give the corrected mirror reflectivities and the uncertainty, including the statistical uncertainty of the expermental data.