By using Weather Research and Forecast model (WRF v.3.5), a series of two-dimensional numerical experiments were carried out under the conditionally unstable stratification to investigate the effect of different height, wide terrain and basic air currents of different directions on the rainfall mode and distribution, when the stratified air currents (uniform distribution of the two layer currents with different wind velocity and wet buoyancy frequency) flow over a terrain. Results show that the terrain gravity wave is the main mechanism to trigger the convection, and the features (amplitude and wavelength) and propagation of the terrain gravity wave are affected by the terrain and environmental flow. When the strong air currents flow over the high and steep mountain, it is easier to recognize the gravity wave located in the lee side of mountain, and a number of types of precipitation modes can be detected, or vice versa. The strength and distribution of rainfall depend on the angle between air currents and mountains because of changes in forced uplift rate and wave stability.