Abstract: Using multi-source observation data, this study analyzed two heavy rainfall events (referred to as "9.27" event and "6.18" event) that occorred at the southern foot of Daba Mountain in northeast Chongqing on September 27, 2017, and June 18, 2018. The similarities and differences of the two events in circulation background, environmental conditions, and topographic action mechanism were compared. The results are as follows: (1) The "9.27" event was a frontal rainstorm, while the "6.18" event was a warm-sector rainstorm. Both were affected by the eastward movement of the 500 hPa trough, low-level shear, low-level jet, and surface convergence line. The differences in location and intensity of the surface convergence line lead to the differences in the fall area and rainband pattern of the two rainstorms. (2) Both events began with weak convective instability and weak uplift conditions. The convective instability increased significantly in the afternoon during the "6.18" event. In both events, water vapor transport channels from the South China Sea were established, with stronger water vapor transport and convergence intensity being found in the "9.27" event. (3) The mechanisms of topographic effects during the two rainstorms were different. During the "9.27" event, the topographic uplift of Guanmian Mountain intensified the thermal contrast near the front, enhanced baroclinic instability, and lifted the warm and wet air to strengthen the water vapor convergence. Under the triggering of the surface convergence line, four convective cells developed and successively passed through the heavy rain area in the north of Kaizhou, forming the "train effect". During the "6.18" event, the dynamic uplift and thermal forcing of the Yangtze River valley and the mountains on both sides caused a high wind speed area near the surface of the river valley, enhanced surface convergence, and triggered several convective cells to move eastward along the Yangtze River Valley. Subsequently, under the topographic effects of Longwangshan Mountain in the east of Fengjie, the development of convective cells was enhanced and remained stable with little movement, resulting in heavy rainfall along and north of the Yangtze River.