Abstract Polycyclic aromatic hydrocarbons (PAHs) play important roles in the formation of combustion generated particles such as soot, but many details of the formation and growth of the PAHs are not yet completely understood. A novel phenyl addition/cyclization (PAC) mechanism has been suggested for the PAHs growth by Koshi et al. based on their experimental result and this PAC mechanism is theoretically investigated in the present work. B3LYP/6-311G(d,p) calculations are used to optimize the geometries of equilibrium and transition state structures as well as to obtain kinetic parameters with the single-point energies being calculated at BMK/6-311+G(3df,2p) level. Conventional transition state theory (TST) with Eckart tunneling correction is employed to calculate the rate coefficients in a temperature range from 300 to 2000K for all the elementary reactions involved in the formation of triphenylene from C6H5 addition to C12H10. Our calculated rate coefficient of the phenylation reaction of biphenyl is consistent with available literature value.