This subject improves light source capability of the soft X-ray beam line 4B7B on the Beijing synchrotron radiation facility (BSRF) by restraining the low energy X-ray in high energy range and the higher-harmonics wave in every energy point. This light source has harmonics wave less than 1%, energy resolution of more than 3000. Some researches on calibration of X-ray detector (XRD) sensitivity, mirror reflectivity, filter transmittance on the soft X-ray beam line 4B7B are performed. The results show that the uncertainty of XRD sensitivity is less than 3%, the uncertainty of mirror reflectivity is less than 3.5%, and the uncertainty of filter transmittance is less than 1%.