<p>Understanding the interaction between petroleum coke and biomass during their co-gasification is important for advancing this technology. This study employed biomass pre-treatment to decouple the contribution of the alkali metals and volatiles on the interaction between biomass and petroleum coke. The results indicate that during the co-gasification, the antagonistic effect exists initially due to the high gasification reactivity of biomass. The synergistic effect is observed obviously in the later stage of gasification, and slightly increases as the process progresses. Biomass volatiles cause the antagonistic effect, whereas alkali metals significantly promote the synergistic effect with their effect peaking before declining. The introduction of alkali metals will interact with the surface functional groups of petroleum coke, forms active intermediates (such as C-O-K), which increases the number of active carbon sites, thereby enhancing the gasification of petroleum coke. The possible coupled influence mechanism between alkali metals and volatiles in the co-gasification of petroleum coke and biomass is also proposed.</p>