The low-temperature oxidation (LTO) mechanism of n-heptane on CeO2 surfaces was investigated in this study employing density functional theory (DFT). Firstly, the adsorption conformations of relevant species were optimized, and the main reaction steps' energy barriers and reaction-rate coefficients were calculated. The results show that the hydroxyl groups of fuel radicals strengthen the adsorption of fuel radicals on CeO2 surfaces. Furthermore, the energy barriers associated with the low-temperature (LT) chain branching pathway of n-heptane on the CeO2 surface exhibit lower values compared to those observed in the gas phase. The presence of CeO2 is also observed to mitigate the detrimental impact of competing reactions on the low-temperature branching pathway of n-heptane. It should be noted that the energy barrier for the decomposition of H2O2 on the CeO2 surface is 32.575 kcal/mol, 33.2 % lower than that in the gas phase, which allows H2O2 to be decomposed much easier at low temperatures. The resultant OH radicals desorb to the intimated gas phase, accelerating the oxidation of fuel molecules in the gas phase. Therefore, n-heptane transitioned to high-temperature ignition more easily and rapidly in the presence of CeO2. The calculation's findings adequately explain the experimental finding that adding CeO2 improves diesel fuel combustion.