Supercritical combustion is a clean and efficient combustion technology that can effectively reduce particulate emissions of gasoline direct injection (GDI) engines. This study proposes a modifying mechanism for simulating supercritical gasoline; this mechanism contains 103 species and 201 reactions and is obtained by modifying the pre-exponential factors of key reactions and adding key reactions on the basis of the original mechanism proposed by our research program. The modifying mechanism is validated by a comparison with the experimental data of Fuel C, Surrogate A, Surrogate B, and each single component (iso-octane, n-heptane, and toluene). The simulation results agree with the experimental results, and the modifying mechanism can predict the various tendencies of ignition delay times with pressure and temperature. The modifying mechanism is further validated by a comparison with the detailed mechanisms proposed by Cancino and JCG et al. The comparison confirms the higher prediction accuracy of the modifying mechanism, which can promote the study of supercritical combustion process in cylinder.