Reproducibility of electrical conductivity of low density polyethylene (LDPE)/carbon black (CB) during the heating/cooling recycling was studied. The melting behavior and volume expansion behavior of the composites were investigated with differential scanning calorimetry (DSC) and press-volume-temperature (PVT) analyzer, respectively. It is found that reproducibility of PTC effect of the LDPE/CB composites was effectively increased after radiation crosslinking. PTC intensity of the gel of the composites decreased greatly as compared with the irradiated composites. This suggests that the volume expansion of the sol at the melting point of the polyethylene played an important role in the PTC effect.