Thermochromic phase change insulating composite can realize a series of advanced functions under electrothermal stimuli, which has been widely applied in numbers of intelligent electrical and electronic devices. However, due to the confined structure of thermochromic phase change insulating composite, the trap characteristics cannot be analyzed by current interface models of nanodielectrics, inhibiting the scientific improvement of dielectric reliability under the electrothermal stress. In this paper, the trap characteristic and mechanism of thermochromic phase change epoxy composites are studied by the isothermal surface potential decay (ISPD) and the Kelvin probe force microscopy (KPFM). Results show that the variation trends of trap characteristics after introducing confined structures are opposite at 30℃ and 70℃, which could derive from the confined phase change or the confined interface. Theoretical analysis shows that the influence of confined phase change on temperature dependent trap characteristics is inconsistent with experimental results, which could not be the essential reason influencing the trap characteristics. KPFM in-situ characterization directly verifies the existence of potential barriers in the confined interface, which originates from the contact electrification mechanism. The temperature dependent charge quantity variation due to contact electrification at the confined interface could impact the barrier height, which substantially affecting the temperature dependent trap characteristics.