Abstract: This study focuses on the preparation and thermal insulation performance of paraffin/diatomite-based phase change energy storage mortar. By activating diatomite and mixing it with paraffin, a composite phase change material is prepared and then incorporated into cement mortar. The results show that as the amount of phase change material increases, the thermal conductivity of the mortar decreases, the heat storage coefficient drops, but the insulation performance is significantly improved. Simulation tests indicate that phase change mortar can effectively regulate indoor temperature and reduce energy consumption.