A customer-designed mini closed pressure vessel test (MCPVT) consisting of a pressure sensor and a temperature sensor connected to recorder was applied to evaluate the isothermal stability along with the formation of hydroperoxide in the ethyl t-butyl ether (ETBE) oxidation process at low temperatures. A new type of hydroperoxide, named 1-tert-butoxy-ethyl hydroperoxide (TBEHP), was separated from ETBE oxidation products via column chromatography, which was further characterized by mass spectrometry (MS), H-1 and C-13 nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR). The thermal characteristics of TBEHP were assessed via differential scanning calorimetry (DSC). Results showed that the exothermic onset temperature (T-0) and thermal decomposition heat (Q(DSC)) of TBEHP were 99.12 degrees C and 1523.89 J.g(-1), respectively. Moreover, a jet-stirred reactor (vessel volume: 500 mL) was used to evaluate the explosive risk of ETBE oxidation. The corresponding result indicated that detonation would arise in conditions of reaching system temperature of 140.0 degrees C, sample mass of 5.0 g, and oxygen pressure of 1.0 MPa, respectively. Finally, it was confirmed that ETBE thermal oxidation was a three-step exothermic reaction including the formation of hydroperoxide by absorbing oxygen, followed by the thermal decomposition of hydroperoxide, and subsequently deep oxidation reactions or detonation caused by reactive free radicals.