This work attempts to investigate the combustion mechanism, reactivity, and coking performance of six octane isomers using reactive molecular dynamics (ReaxFF MD) simulations and the VARxMD code. The kinetic analysis results were firstcompared with the experimental data to verify the validity of the simulation results. It was found that the combustion of six isomers mainly involves C−C bond cleavage, isomerization reactions, dehydrogenation, and oxidation. The cleavage of C−C bonds is the dominant route of initial reactions in combustion. While the isomerization reaction is a major distinction between normal and branched alkane isomers. The formation mechanism of coke precursors was further discussed by pathway analysis. The results showed that the existence of branch chains increases the possibility of the formation of coking precursors, and monoethyl isomers show the highest generation trend. The methyl substitution location also has an obvious effect on the formation mechanism of coke precursors. For meta-methyl isomers, coke precursors are formed by dehydrogenation of macromolecules at high temperature, while those are caused by collisions between carbon atoms for ortho-methyl isomers. The product distribution showed that the number of ethylene groups in n-octane combustion is larger than that of other isomer systems, while there is more CO formed in 2,2,3,3-tetramethylbutane combustion. For reactivity, the n-alkane is more reactive than other isomer systems, and increasing the number of methyl substitutions also enhances the reactivity of branched isomers for multimethyl isomers. Hopefully, the mechanism information obtained in this work could improve the understanding of differences in combustion of octane isomers and provide insights into the structural effect during the fuel combustion process at the molecular level.