The pre-launch calibration of the water vapor channel onboard FY-2B geostationary meteorological satellite was made in the Lab's vacuum container.The change of sensor's characteristics post-launch is normally monitored by the onboard blackbody.However,since the blackbody calibration path adopts different objective optic path,it is hard to make the in-orbit absolute calibration for the WV channel of the satellite.The pre-launch calibration of FY-2B's WV channel was introduced,and the calibration processing method with the quantized relation derived from in-orbit electronic calibration,as well as the inter-calibration for the channel 12 of HIRS/3 aboard NOAA-17 was also deseribed.