Infrared thermal imager is a powerful instrument for temperature measurement and nondestructive testing, but the measurement accuracy of infrared thermal imagers is easily affected by other factors. Aiming at the influence of dust in the optical path between the measured object and the infrared thermal imager, this article proposes a compensation model based on the infrared temperature measurement principle. Then, dust transmittance and reflectance, two important parameters but difficult to determine in the compensation model, are determined based on the reference body. Furthermore, an approximate compensation method is derived to increase the applicability of the compensation method, and its application requirement is also studied. The effectiveness of the proposed compensation method is demonstrated in a blackbody furnace experiment and a water cup experiment.