In this work, ab initio based NNPESs are developed and applied in reactive MD simulations to study the mechanisms of the formation and growth of PAHs and soot inception. MD simulation revealed the detailed mechanisms about the formation of monocyclic and bicyclic PAHs from small hydrocarbon molecules and radicals, detailed reaction paths leading to the formation of PAHs containing three to nine aromatic rings, and reaction paths leading to soot inception.