In order to prepare low-temperature composite phase change materials based on blast furnace slag with good performance, based on vacuum impregnation method, the modified blast furnace slag and graphene oxide/paraffin composite phase change materials are used as main raw materials, and the microstructure, thermal conductivity and latent heat of phase change of the materials are analyzed by SEM, Hot Disk and TG-DSC to find out the molding mechanism of the materials. The results show that the degree of influence in descending order on the thermal properties of low-temperature composite phase change materials based on blast furnace slag is the mass fraction of composite phase change materials in modified blast furnace slag, the type of modified blast furnace slag and the mass fraction of graphene oxide in composite phase change materials. Considering comprehensively, with acid modified water quenching blast slag as the carrier, when the mass fraction of graphene oxide in the composite phase change materials is 4% and the introduction amount of the composite phase change materials in the carrier is 30%, the composite material has the best performance. The thermal conductivity of the material is 0.59 W/(m·K), which is about 3 times that of acid-modified blast furnace slag or alkaline-modified blast furnace slag, and the phase change enthalpy is about 98.82% of that before thermal cycle, the latent heat of melting and solidification are 112.27 and 82.16 J/g, respectively, and the melting temperature and solidification temperature are 50.12 and 55.45 ℃, respectively.