Abstract: This paper focuses on radiometric calibration of triple-band optical imaging system which includes near ultraviolet (300 nm~380 nm), visible (380 nm~760 nm) and near infrared (760 nm~1 100 nm) ranges. The radiometric calibration system was set up, the mathematical model was established and the radiometric calibration experiment was conducted. As the optical system operated at three wavebands, technique of sub-band radiometric calibration was adopted. The calibration data were fitted by linear least squares and then the algorithm was modified. At last the calibration data were processed. Experimental results verify the calibration accuracy of two methods. The calibration curve obtained by the modified algorithm is with higher accuracy. The relative error of measurements can be less than 5%, which meets the needs of actual projects.