The coking phenomenon of coker gas oil (CGO) feedstock during fluid catalytic cracking (FCC) using a commercial equilibrium catalyst was investigated. Different types of coke formed via coker gas oil (CGO) catalytic cracking were also analyzed. The coke formed was composed of adsorption coke (C-ad), dehydrogenation condensation coke (C-dh), and hydrogen transfer coke (C-ht). C-ad, derived from nitrogen compounds, adsorbed on the acid sites of the catalyst and accounted for 37 wt % of the total coking content under conventional reaction conditions. C-dh was formed by the dehydrogenation condensation of polycyclic aromatic hydrocarbons and accounted for about 43 wt 96 of the total coking content. The coking content of C-ht was greatly determined by the degree of the secondary reaction. Coke selectivity can be decreased and C-ht yield can be controlled by simultaneously increasing the reaction temperature and shortening the reaction time.