In this paper, a numerical calculation and application analysis of composite phase change material masonry mortar applied to wall parts are performed during the research process. Instead of the conventional "sandwich" phase change material wall, our research group mainly uses phase change materials in the wall parts to build masonry joints to reduce the thermal bridge effect. The influence of masonry joints on the heat transfer of the wall is demonstrated. A quantitative description of the transient heat transfer coefficient is obtained to measure the heat preservation performance of the phase change material wall. Furthermore, the influence of different proportions of phase change materials on the wall heat transfer in different external environments is discussed, supplemented by the influence of the working range and sensitivity on the heat transfer. In summary, the use of phase change materials in the construction of masonry joints is a great innovation for conventional "sandwich" phase change material walls, optimizing the form, the thermal bridge effect and the heat preservation performance of wall parts. The quantitative description of the transient heat transfer coefficient expands the development of wall heat transfer theories. In addition, the conclusions are of great guiding significance for the structure and the phase change material's blending proportion for the innovative heat preservation phase change material wall.