By integrating a reduced n-heptane oxidation chemical kinetic reaction mechanism in a multidimensional computational fluid dynamic solver, simulation of the turbulent diffusion reactive flow inside the direct injection (DI) diesel combustor through compression and expansion stroke were implemented. Coupled with the soot kinetic model by the method of moments, the soot formation is modeled simultaneously with a gas-phase flame. Under fuel lean flame, orders of magnitude of the multi-ring polycyclic aromatic hydrocarbon (PAH) intermediate molar fraction are very small. Though soot surface growth is overwhelmed quickly by oxidation under current modeling conditions, the simulated soot number density and average diameter curves are consistent with experimental results. A detailed soot kinetic mechanism is a prospect for further research in computational fluid dynamics (CFD) modeling.