Abstract: Based on ERA5 reanalysis data, GPM precipitation data and WRF model, a synoptic dynamic analysis and numerical experiment are conducted to analyze gravity wave characteristics of a heavy rainfall in Sichuan Basin on 2 July and 3 July in 2023, in order to deepen the understanding of the mechanism of gravity wave affecting the basin rainstorm, and to discuss the cause of topography affecting the excitation of gravity wave and water vapor condition. Results indicate that precipitation exhibits fluctuating characteristics, influenced by several favorable factors, including water vapor flux convergence, strong vertical wind shear, and is affected by jet stream, shear line and upper trough. The upper gravity wave is initiated by shear instability and non-equilibrium flow mechanisms at the downslope of the southern Basin, propagating northeast. At night, the disturbance in geopotential height over the plateau extends into the upper troposphere, resulting in a stronger gradient of geopotential height between the plateau and the Basin. With the decrease in solar radiation heating, the influence will extend to 250 hPa, which will also impact the excitation of gravity waves. The low-level gravity wave is generated by the sloping topography and propagate northward, with two waves coupling in phase during the night. During this period, the release of unstable energy in the precipitation area is significantly enhanced. This phenomenon also suggests that in-phase wave coupling may be a contributing factor to the increase in precipitation at the energy level. Numerical experiments conducted on flattening various mountain ranges in the southern part of the Basin indicate that precipitation initially occurs in the transition zone between the northern foothills and the plain. The southern topography of the Basin enhances the vertical wind shear through the downhill acceleration and the disturbance geopotential height gradient caused by the radiative cooling difference, which affects the gravity wave excitation region and the precipitation region. Due to the influence of upper airflow in the early stage of rainstorm, 350 hPa simulates ice crystal large value area originating in the downhill region of terrain, and the origin of ice cloud bands shifts to the south with the slope position of each test scheme. In addition, the horizontal convergence of water vapor primarily occurs in the plain. Therefore, favorable water vapor conditions in the Basin combined with the specific circulation characteristics make the main precipitation of this process not occur in the slope and mountain area in the south of the Basin as the normal mountain rainstorm, but under the combined influence of gravity wave transmission to the north and multiple systems in the middle and low levels, the belt rainstorm occurs in the plain and hilly areas of the central Sichuan Basin.