Polycyclic aromatic hydrocarbon (PAH) is suggested as an origin of particulate matter (PM) in exhaust gas of diesel engine. In present study, aggregation processes of chemical species in the exhaust gas are numerically simulated by molecular dynamics (MD) method. The simulated exhaust gas consists of H_2O, CO_2, N_2, O_2 and Coronene. Aggregation kinetics of chemical species is quantified by internal energy under constant temperature and volume ensemble. The aggregation rates of Coronene, H_2O and CO_2 decrease with temperature. No chemical species aggregate over 450K except for Coronene. The aggregation rate increases with molar fraction of Coronene.