Thermochromic phase change insulating composite can possess a series of advanced functions under electrothermal stimuli, which has been widely applied in a great number 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 existing interface models of nanodielectrics, which inhibits 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). The results show that the variation trends of trap characteristics after introducing confined structures at 30 ℃ and 70 ℃ are opposite, 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 cannot be the essential reason for affecting 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 variation of temperature dependent charge quantity due to contact electrification at the confined interface can affect the barrier height, which can substantially affect the temperature dependent trap characteristics.