The stability evaluation of artificial submarine slope under wave load is a primary concern in the construction of offshore structures such as submarine pipelines and immersed tunnels. Aiming at this issue, an integrated Finite Element Method (FEM) model of wave-seabed interaction is proposed to investigate the effects of wave action on the wave-induced slope stability of the temporary trench. The Reynolds-Averaged Navier-Stokes (RANS) equations are adopted to describe the wave motion in the fluid domain, while the seabed domain is described using the Mohr-Coulomb constitutive model. The wave-induced seepage pressure near the slope is determined by Darcy's law and considered as an external load in the analysis. The stability of the temporary slope is evaluated by the means of shear strength reduction. The present numerical model is firstly validated through the comparison with the analytical solution and the experimental data available in the literature. The integrated numerical model is then applied to a practical engineering application, including a new evaluation method of stability for the trench slope excavated temporarily for the fully-buried submarine pipelines at an actual site. The results indicate that the stability of submarine slope is closely related to the dynamic wave pressure from the upper seawater. The minimum of FOS (factor of safety) corresponding to the most dangerous situation is introduced as the stability index for the slope with specific slope ratio in the whole process of dynamic wave loading. Additionally, the wave-induced seepage pressure should be considered as external load in the design for the seabed with large permeability such as sandy soils.