Abstract: Dicumyl peroxide (DCP) was used as the research object, and the influence of the impurity Cu²⁺ at different concentrations on its thermal stability was studied using an adiabatic accelerated calorimeter (ARC). The thermal parameters of DCP in adiabatic decomposition process, such as initial decomposition temperature (T₀), maximum exothermic temperature (T_f), adiabatic temperature rise (ΔT_ad), maximum temperature rise rate (m_m), were obtained by data analysis, and the decomposition activation energy (E_a) was obtained by fitting. At the same time, the thermal inertia factor (ϕ) was used to correct the test data. The results showed that the existence of Cu²⁺ had an obvious effect on the adiabatic decomposition parameters of DCP. For example, the initial decomposition temperature of commercial DCP was 101.5 ℃, while that of DCP containing 0.97×10^–3% and 4.87×10^–3% Cu²⁺ is 90.1 ℃ and 90.3 ℃, respectively; with the increase of Cu²⁺, the activation energy of DCP decreased, which was 164.47, 162.24 and 156.83 kJ/mol, respectively. This indicated that the existence of Cu²⁺ made the thermal decomposition of DCP easier and increased the risk of thermal decomposition of DCP.