The reflectivity of grazing soft x-ray planar mirror is studied.The Beijing Synchrotron Radiation Facility-3W1B beam line with beam current 40—120 mA,the storage ring electron energy 2 GeV,photon energy 50—1500 eV are used.We have improved the calibration method.The x-ray diode detectors of planar mirror facility are replaced by AXUV-100.Therefore,2 to 3 orders of magnitude for the ratio of signal to noise can be increased,and the calibration region from (150—270 eV)to (50—1500 eV)is expanded.The reflectivity calibration curves for C,Si,Ni,and Au planar mirror in different grazing angles are given.Finally,the values obtained in experiment and calculation are compared and analyzed.