The core concept that runs through Badiou's philosophy is the event. From the early Theory of the Subject, through Being and Event, to Logics of Worlds, and then to The Immanence of Truths, although Badiou adopted different methods and ideas, the only constant is the core position of the event in his philosophy. Among them, Being and Event and Logics of Worlds are the two most critical books of Badiou on the issue of the event. Badiou believes that the former is to demonstrate the possibility of the event from the perspective of mathematical ontology, while the latter proposes how to hold the world from the perspective of phenomenology, reflecting the understanding of events developing from ontology to phenomenology.