Landslide-induced water waves (LIWWs) are a combination of a landslide and its induced tsunami wave, which can cause significant damage to coastal areas and adjacent coastlines. Compared to earthquake-generated tsunamis, LIWWs may have relatively shorter wavelengths and higher local wave amplitudes, which make them highly dispersive and nonlinear. LIWWs can also induce large runups along adjacent coastlines where human settlements are located, posing a significant flood risk, especially in restricted water bodies like lakes, dam reservoirs, bays, and fjords. In the mountain area, sliding material may decrease the efficient capacity of artificial reservoirs and increase reservoir sedimentation. Therefore, understanding the physics of LIWWs is essential for flood risk management, hazard assessments for engineering and environmental projects, and reservoir management. However, the complex dimensions, phases, and mechanics of LIWWs make them challenging to analyse, and reliable methods are needed to study the dynamic processes of LIWWs, including the generation, propagation, runup, and flooding of the induced tsunami. In this study, the 2D coupled Discontinuous Deformation Analysis (DDA) and Smoothed Particle Hydrodynamics Method (SPH) are used for modelling the dynamic process of the rockslide-induced tsunami in a dam reservoir. DDA is a powerful technique for modelling blocky systems, while SPH is one of the most popular numerical methods for analysing the mechanical behaviours of flow-like materials. The interaction between the DDA block and the SPH particle is realised through the penalty method. The sliding mass and the dam are divided into small DDA blocks. The simulation presents the processes of the LIWW hazards, including slide initiation, motion, interaction with water, impulsive wave generation, propagation, runup, overtopping, and inundation of the sliding mass.