Π-shaped composite girder is a typical blunt section. When airflow passes through it, the phenomenon of flow separation and vortex shedding is more apparent than in streamlined sections, leading to wind-induced vibration becoming one of the control design factors for Π-shaped girder cable-stayed bridges. Flutter stability is also an important content in wind-resistant design for cable-stayed bridges. Flutter derivative is one of the important parameters in flutter stability analysis, which is traditionally determined by wind tunnel tests that consume a lot of time and money. Based on the Liujiang Bridge, this paper introduces CFD technology into the study of Π-shaped composite girder cable-stayed bridge flutter stability, identifies the vibration derivative of Π-shaped composite section using CFD technology, extends the two-dimensional flutter analysis method to a three-dimensional, and develops a corresponding flutter analysis program. The research results show that conducting long-span cable-stayed bridge flutter performance research using CFD technology is feasible.