In order to address the spatial and temporal contradiction in wall energy supply and further enhance building comfort, phase change microcapsules (Micro-PCM) were incorporated into cementitious materials to develop a phase change mortar, leveraging the advantages of both phase change materials and cement. A layer of phase change mortar was applied onto the surface of a wallboard, which was subjected to simulated solar radiation using incandescent lamp heating. The thermal performance of the phase change thermostatic wall board under solar radiation was experimentally investigated, while numerical simulations were conducted using COMSOL software. The results demonstrate that with the increase of Micro-PCM content, the heat storage capacity of phase change thermostatic wall board increases. When the Micro-PCM content reaches 40% (volume fraction), compared to ordinary wallboards, there is a reduction in peak temperature by 5.166 ℃, delay in peak temperature time by 145 min, decrease in peak temperature amplitude by 4.509 ℃, and reduction in peak heat transfer by 22.202 W/m2. Furthermore, when phase change mortar is placed within aerated concrete block walls, there is a decrease in peak temperature amplitude to 2.38 ℃ and maximum instantaneous heat transfer reduced by 1.61 W/m2. The developed phase change mortar exhibits excellent heat storage performance along with sufficient mechanical strength for application on envelope structures to effectively regulate temperatures.