In order to understand the characteristic of water tree growth for cross-linked polyethylene (XLPE) at different temperatures, here, a new possible explanation is presented for the different characteristic at different temperatures. Water tree aging experiments were performed, respectively, at 0, 20, 40, and 60°C. The shapes of water trees were observed by an optical microscope, and the sizes of water trees at different temperatures were recorded. Based on the molecular dynamics and polymer orientation, the new possible explanation for the characteristics of water tree growth is proposed at high or low temperatures. According to the experiments, the rate of water tree growth first decreases and then increases with the rise of temperature and the transition temperature is about 40°C. The behaviours of thermal motion and orientation of molecules can both influence the water tree growth. The water tree growth at high temperature is mainly determined by the thermal motion, while the water tree growth at low-temperature is mainly affected by the behaviour of molecules orientation.