Abstract: The stacker–reclaimers are critical pieces of equipment widely used in ports, in mines, and in power plants. During operation, their long boom structures are subjected to heavy operational loads, leading to large deformations and pronounced nonlinear dynamic responses. To accurately characterize the mechanical behavior of the boom and to investigate its nonlinear dynamics under various operating conditions, proposed is a rigid–flexible coupled dynamic modeling approach for large-scale stacker–reclaimers. Considering the slender and highly flexible nature of the boom, it is modeled as a flexible structure using geometrically exact beam elements, while the counterweight—characterized by its high stiffness, by a small deformation, and by a weak coupling with other components—is represented as a rigid body. The driving mechanisms are incorporated in a unified manner through constraint equations. Based on the Euler-Lagrange formulation, the system dynamic equations are established and solved using the Newmark time integration scheme. Numerical simulations under representative operating conditions are conducted to analyze the trajectory of the bucket-wheel center and the stress evolution in the hoisting cables, revealing the dynamic response characteristics of the boom system. The research results demonstrate that the model proposed can accurately capture nonlinear transient dynamics associated with large deformations, providing a solid theoretical foundation for structural optimization and control strategy design of large stacker–reclaimers.