Abstract: The phase change heat transfer performance of the topology optimization model was analyzed and studied using numerical simulation methods. Focusing on models where natural convection serves as the primary heat transfer mechanism, the effects of different mesh sizes on the topology optimization results and their phase change heat transfer characteristics were examined. The topology-optimized models were post-processed and compared with a baseline model to analyze differences in melting performance. The results indicate that, compared with the baseline model, the optimized models significantly reduced the complete melting time of the phase change material. Under natural convection conditions, the optimized fin structures were primarily concentrated in the upper and lower regions of the unit. As the mesh size decreased, the number of fin branches on the left and right sides gradually increased, with a maximum difference in melting time of 16.9% observed among the natural convection models. Additionally, the morphology and distribution of fin structures had a pronounced influence on the development of natural convection. When the mesh size was 0.2 mm, the optimized fin structures exhibited a broader distribution and more branches, however, which suppressed the development of natural convection circulation, leading to a bigger complete melting time than that of the model with a 0.6 mm mesh size. Therefore, comprehensively considering the morphology, arrangement, and coupling effects of fin structures on natural convection is of great significance for enhancing phase change heat transfer performance.