Abstract: Based on Black Body Temperature (TBB) data of Fengyun 2G (FY-2G) geostationary meteorological satellite and precipitation data of Panxi region of Sichuan Province, this study analyzes the spatiotemporal distribution characteristics and their relationship with convective clouds and heavy rainfall in mountainous areas of southwestern Sichuan, under the influence of the western Sichuan Plateau on the southeastern side of the Qinghai–Xizang Plateau, from June to September during 2019–2021. The results demonstrate the following: (1) The Ganzi Prefecture (28°–32°N, 98°–103°E) of the western Sichuan Plateau in the southeastern part of the Qinghai–Xizang Plateau is an active center of convection, and convective clouds mainly move southward following the northwest path from the western Sichuan Plateau. After arriving at the Panxi region in mountainous areas of southwestern Sichuan, the convective clouds continue to move in three directions: Eastward, southeastward, and southward. These pathway areas are also the key formation areas of heavy precipitation in mountainous areas of southwestern Sichuan. (2) Heavy rainfall related to the influence of the northwest path in mountainous areas of southwestern Sichuan is more notable in June–July than in August–September, being highest in July and lowest in September. Moreover, the frequency of heavy precipitation in June–September is highest for the southeastward-moving type of convection, followed by the southward-moving type, with the least for the eastward-moving type, hence exhibiting prominent intermonthly variation. (3) In the key area of the western Sichuan Plateau, because of the typical north–south ridges of the Hengduan Mountains, Shaluli Mountains and Great Snow Mountains form the generation area of the initial convection for heavy precipitation under the northwest path influence at 1400–1500 BJT (Beijing time), while the characteristics of initial convection, influencing duration, and precipitation peak differ between the eastward-, southward-, and southeastward-moving convections. (4) The hourly short-duration heavy precipitation under the northwest path influence exhibits obvious characteristics such as single precipitation peak and night rain, while the eastward-, southeastward-, and southward-moving convections exhibit certain differences in terms of abruptness, duration, and intensity of heavy precipitation. (5) Although both the initial convection and the convective clouds that first affect heavy precipitation along the northwest path in mountainous areas of southwestern Sichuan originate from the key area of the western Sichuan Plateau, the features of convective location, development impact, precipitation distribution, and precipitation center are different, depending on whether the subsequent convection moves eastward, southeastward, or southward. The reserrch is very significant to further comprehend the mesoscale and microscale convective activities and the influence thereof on heavy precipitation in complex mountainous areas in the topography of the Qinghai–Xizang Plateau.