A general model for calculating the infrared-radiation intensity of extended aerial targets and small infrared targets is proposed. The model eliminates the influence of background bias, which depends heavily on ambient temperature, and can effectively improve the measurement accuracy of infrared-radiation characteristics of aerial targets in complex and changeable environments. The calculation of small-target infrared radiation intensity is discussed based on the characteristics of dynamic infrared test data of a type of aerial target. The results show that the contribution of the apparently atmospheric radiation intensity to the total radiation intensity is negligible for small medium-wave infrared targets. A simplified model used to calculate total radiation intensity is presented, but it is not applicable for small-target long-wave infrared radiation. The dynamic small-target infrared test data and the extended-target data are processed and compared with theoretical results, and the results verify the correctness of the model.