The dual-crane cooperative lifting system demonstrates significant advantages in lifting large and complex components. However, due to the inertial effects of the payload and the dynamic motion characteristics of the lifting equipment, it is prone to causing the payload to swing, which affects the system’s stability and safety. To address this issue, this paper establishes a dynamic model for the dual-crane cooperative lifting system based on the Lagrangian equation. Through simplified assumptions, the complete nonlinear dynamic equations are derived, and the model's validity is verified using Adams simulation software. The simulation results show that the established model can accurately describe the system’s dynamic behavior and reveal the impact of wire rope length and initial angle on the payload's swinging characteristics. Further analysis indicates that a longer steel wire rope increases the swing period and amplitude of the payload, while a larger initial angle significantly raises its swinging frequency and amplitude.