Abstract: The wave-absorbing materials are widely used in wireless tests for microwave payloads. In a thermal vacuum environment, the wave-absorbing apparatus works as an external heat flux simulator in thermal vacuum or thermal balance tests. It is composed of an array with large number of thin mini pyramids, so a huge computational resource is required in its design. A simplified thermal analysis model is required for optimizing the engineering design. Based on the volume-average approach, an equivalent thermal model is established for the wave-absorbing structure with empirical coefficients. The analytical results of the transient temperature and the thermal flux, as well as the temperature distribution, are compared between the equivalent model and the detailed (actual structure) model, and the accuracy of the equivalent model is validated. The proposed model enjoys an enhanced computational efficiency for engineering applications.