In order to further improve the heat storage capacity of solar greenhouse walls and improve the indoor thermal environment, the application of paraffin-expanded perlite composite phase change material (PCM-PE) in greenhouses was studied. The transient system simulation program (TRNSYS) was used to build a model of a fabricated composite wall solar greenhouse, and measured data from sunny and cloudy days were used to verify the accuracy of the model. The model was used to analyze the changes in indoor temperature and the unit cost of the greenhouse after PCM-PE was added to the inner surfaces of the structures, such as the north roof, the side walls, and the north wall, respectively, as well as the optimal thickness of the greenhouse when PCM-PE was added to the north roof, the side walls, and the north wall. The results show that the addition of PCM-PE to the inner surfaces of different greenhouse structures has a significant effect on increasing the average indoor temperature, and the addition of PCM-PE to the inner surfaces of the side walls makes the average indoor temperature increase by 1.32 ℃ on sunny days, with the lowest unit cost of 2 094 Yuan/℃; When PCM-PE is added to the north roof, side wall, and north wall with an optimal thickness of 50 mm, the average indoor temperature and the average temperature of the north wall increase by 3.9 ℃ and 3.7 ℃ on sunny days, and by 2.2 ℃ and 2.3 ℃ on cloudy days, respectively; After adding 50 mm PCM-PE, the heat transfer coefficient of the greenhouse wall is reduced by 15% and the thermal resistance increases by 9.9% compared with that of the test greenhouse, which has a positive effect on maintaining the indoor temperature and reducing the energy consumption of the greenhouse. The effect of applying PCM-PE to different structures of greenhouses is analyzed considering the unit cost, which provides some reference for constructing greenhouses with good economy and high heat storage performance.