Abstract: This Paper describe the in-flight radiometric calibration for thermal channels of FY-1C and FY-2B meteorological satellite sensors using Qinghai lake, water surface radiometric calibration site. The radiance of water surface measured by CE312, and then performed atmosphere correct including gas absorption and path radiance which computed by radiance transfer code MODTRAN37, predict the radiance in the satellite sensor entrance pupil. At the same time the spectral response of Satellite sensor and that of ground-based sensor are coupled. At last the apparent radiance of sensor spectral channels are compared to the digital count of satellite's output to give the calibration coefficient. Several calibration is conducted for the satellite thermal sensors of FY serial satellites. The result show the difference between in-flight and on-board calibration is about 5%, equivalent to a brightness temperature of 3 K.