Abstract: Based on the FLUENT computational fluid dynamics software and its secondary development function, as well as the VOF (Volume of Fluid) multiphase flow model, a stratified numerical water flume that simulates the propagation of oceanic internal waves is established with the standard k\text-\varepsilon turbulence model. In the numerical water flume, two-layer density-stratified fluid is set up, and the flapping plate method is used as the wave maker. Different combinations of density differences and water depth ratio between the upper and lower fluid are numerically simulated under two boundary assumptions of rigid lid and free surface at the still water level, and their numerical results are compared to their theoretical ones respectively. It is found that the differences of the densities of upper and lower fluid do not significantly influence the consistency between the numerical results and theoretical ones, and that the differences of the depths of upper and lower fluid significantly influence the numerical results. When the depth of the upper fluid is low, the notable vertical velocity appears at the interface between water and air under the assumption of free surface. Under the two assumptions at the still water level, the calculated horizontal velocities both reflect the nonlinear effect when the depth of the upper fluid is low, but hardly reflect the nonlinear effect when the depth of the lower fluid is low. Considering the fact that the depth of the upper fluid is much lower than that of the lower fluid in the actual ocean circumstance, it is more reasonable to adopt the assumption of free surface at the still water level, especially when the internal solitary waves with a larger amplitude are numerically simulated.