A radiation calibration method is proposed for the compensation of output gray values of an infrared spectrometer system based on the variation in ambient temperature. First, the reasons for the output gray-value shift of the infrared spectrometer system in the process of radiation calibration and measurement are analyzed; subsequently, the functional relationship between the change of drift and ambient temperature radiation is obtained. Then, the laboratory radiation calibration equation and radiation calibration equation at different ambient temperatures after compensation are determined by experimental radiation calibration using the uncooled long-wave infrared grating spectrometer developed in our laboratory. Finally, the accuracy of the radiation measurement using the compensated radiation calibration equation at different ambient temperatures is experimentally verified. The results show that the output gray-value error of the spectrometer system can be significantly reduced by drift compensation at different ambient temperatures, and the error is less than 2.4%. The measurement accuracy of the uncooled long-wave infrared spectrometer for infrared radiation is greatly improved in this research.