With the development of the offshore construction industry， many 100-ton large structures need to be transported to the assembly site by sea. In the unloading and transfer process， the barge is affected by the wind， waves， and currents， which will produce six-degree-of-freedom motion， so that the suspended load moves relative to the ground， causing the suspended load to sway， which affects the crane operation， resulting in operational inefficiencies and a series of potential safety hazards. In this paper， for hoisting and unloading of large structures， numerical simulation is used to analyze the barge movement and the dynamic characteristics of the lifting process， to assess in advance the safety of the operating envelope and sling forces throughout the operation， and to propose countermeasures for the main safety risks， in order to provide reference for the construction of subsequent similar projects.