Submarine landslide is one of the main causes of tsunami disasters. Understanding these events is crucial for improving hazard assessment and early warning systems, which may be used for reducing risks to coastal communities. In this context, we propose a unified method to simulate the landslide initiation, the interaction with its surrounding environmental water, and the propagation of the tsunami wave. Given the enormous difference of scale between the landslide initiation and the tsunami propagation, we propose a multi-scale technique in which the problem is divided into two stages: first, we propose to use the Smoothed Particle Hydrodynamics (SPH) method to solve the submarine landslide problem and its interaction with the environmental water. Then, we couple that solution to a tsunami propagation model based on the SPH solution of the shallow water equation. For the first stage (submarine landslide model), the landslide is treated as saturated soil and the interaction between the soil and the water is calculated as a fluid-soil interaction (FSI) problem. For the second stage (tsunami propagation model), we use the SPH method to solve the shallow water equation in an Eulerian framework. Finally, the coupling between the two stages is done by assigning some particles of the tsunami propagation model to receive wave height and velocity data from the boundaries of the submarine landslide model, which becomes the initial conditions for the tsunami propagation.