In order to improve the imaging performance and image quality of space cameras with an optical focal plane assembly, the radiometric calibration researches in the whole develop process of the space cameras are conducted which include the radiation response performance analysis, the radiometric calibration and screening of the image sensors, the focal plane radiometric calibration, the system-level radiometric calibration, and the applications of radiometric calibration data. The radiometric calibration experiment is conducted for the space cameras with a reflector-based mosaic focal plane. The results show that the vignetting can be effectively eliminated when the image is corrected by using the relative radiometric correction coefficient, and the nonuniformity of the image decreases from 14.1% to 0.4% with an obvious enhancement in the image quality. Moreover, the radiometric response difference between the image sensors is reduced by utilizing the screening of the image sensors and the radiometric calibration of focal plane components, and the relative calibration uncertainty is less than 1.0%.