High-energy–density (HED) fuels (like JP-10) have drawn more and more attention for volume-limited aerospace vehicles to extend the flight range and/or increase the payload. However, their thermal oxidation and deposition performance are still ambiguous. In this work, the dynamics and mechanism of JP-10 thermal oxidative deposition were investigated by the jet fuel thermal oxidation stability tester (JFTOT), ellipsometric tube rater (ETR) and comprehensive two-dimensional gas chromatography coupled with mass spectrometry and flame ionization detector (GC × GC–MS/FID). The results reveal that both the peak deposit thickness and total deposits volume of JP-10 increase with increasing temperature with the apparent deposition activation energy of approximately 71.2 kJ/mol. The deposits on the tube surface have globular structure, and they undergo particle formation, growth, adherence, agglomeration and size reduction during thermal stress. The fine characterizations of liquid products after JFTOT test confirm that the thermal oxidative deposition of JP-10 occurs via a series of radical reactions, such as oxidative decomposition and radical addition, which will be significantly accelerated at higher temperature. Importantly, the stability of alkoxy radical seems to be a significant factor affecting the thermal oxidation stability of HED fuels. This work may shed light on the possible deposition mechanism of HED fuels and will guide the rational design of HED fuels with high thermal oxidation stability.