The Discrete-Module-Beam (DMB) method is applied on a Very Large Floating Structure (VLFS) to perform a hydroelastic analysis under unsteady external loads, including displacement response and structural force response. The hydrodynamic analysis is performed by three-dimensional potential flow theory, and the DMB method is extended to the time domain based on the Cummins equation; the displacement response is restored by the sub beam method. The structure is viewed as a massless free-floating beam, whose external loads are divided into 2 groups according to whether the distribution is known or not. The structural force distribution induced by loads whose distributions are known is obtained directly with an integration of these external loads. For the loads with unknown distribution, a third-order interpolation scheme is implemented after some processing on the original hydroelastic equation. A cargo dispatch case and a plane landing case are calculated. The DMB method is able to give the accurate structural displacement response and bending moment distribution in the initial stage of the loading process and shows an abrupt change on the location where a concentrated force is exerted.