Based on finite element analysis, a typical synchrotron radiation front-end high heat load absorber (fixed mask) is thermally analyzed to illustrate the heat transfer paths and thermal release mechanisms. Based on the finite element model, the steady-state and transient thermal analyses are jointly adopted, focusing on obtaining the thermodynamic behavior of the absorber after being illuminated and heated by the synchrotron beam, as well as cooled by thermal convection (including air convection and cooling fluid convection) and thermal radiation. This paper focuses on analyzing the changes to key indexes, such as temperature and thermal stress, of an absorber subjected to high heat load on the timescale. In addition, the contributions of the previously mentioned different thermal heat release modes to the heat release process are also quantitatively analyzed to elaborate the thermal release mechanisms, which can be pretty helpful for guiding the structural optimization design of such types of components.