Abstract: Composite phase change materials (PCMs) were prepared by melt mixing poly(ethylene glycol) (PEG, molecular weight<1 000) with expanded graphite (EG) as a thermally conductive enhancer, and various effects on the cool storage performance of the PEG/EG composite PCMs were analyzed. The influences of EG content and pressing level on the thermal conductivity of PCMs were investigated by a flash thermal analysis method, their microstructures were determined by scanning electron microscopy, and their cool storage performance was characterized by an engineering survey method to obtain phase transition curves. The results indicated that the effects of EG content and pressing level on the thermal conductivity of PCMs were caused by changing the internal structure of thermally conductive network in the PEG matrix. The cool storage performance was improved with the increase of EG content, and EG also could weaken the influences of coolant content and coolant temperature on the cool storage process.