Theoretical design is very critical for the experimental fabrication of a high-efficiency solar photothermal conversion film structure. However, most softwares are usually limited to the optimization of solar absorption under the normal incident condition, rather than focusing on the criteria of solar photothermal conversion efficiency (PCE). In view of the above problems, the transfer matrix method and the genetic optimization algorithm are used to directly optimize the photothermal conversion efficiency of a multilayered metal/dielectric film structure by changing the thickness of each layer of the film. The effects of the film layer number, solar illuminance, and ambient temperature on tungsten-alumina-based (W/Al₂O₃) multilayered film structures are studied. The results show that the optimal number of film layers is 6 for solar concentration ratio of 1 and 8 for that of 100. These results have important guiding significance in the experimental fabrication of high-efficiency solar photothermal conversion films.