Abstract: The purpose of this paper is to reveal the cognitive mechanisms and factors influencing the degree of coherence of oral discourse output of bilinguals. This study examines the influence of the central executive system on the coherence of spoken discourse of bilinguals through a behavioural experiment. The experiment used two components of the central executive system: working memory capacity and attentional inhibition as independent variables, and nine indicators defined by Coh-Matrix to measure the degree of discourse coherence as dependent variables. Significance analyses showed that working memory capacity and attentional suppression had a significant effect on eight of the nine indicators of spoken discourse coherence, i.e., interreferentiality, lexical specificity, neighbourhood overlap, causality, discourse relevance, verb consistency, logic, and intentional consistency; however, they did not significantly correlate with full-sentence overlap; regression statistics found that working memory capacity and attentional suppression were highly correlated, and that both of them were highly correlated with the degree of spoken content Among the nine indicators of coherence, discourse relevance, intentional consistency and lexical specificity had the greatest influence.