This paper investigates the flooding events caused by heavy precipitation and the corresponding 15 heavy rainfall events in the Sichuan-Chongqing area in the summer of 2020 year and compares them with the situation in the 2006 drought year. In the summer 2020, the western Pacific subtropical high (WPSH) was stronger compared with its climatological mean, and its western edge was beyond 110°E which is to the west of its climatological position. Since the Qinghai-Tibet high extended eastward and was strong, the upper and lower layers worked in concert to maintain the WPSH steadily. The cold air that causes precipitation in the Sichuan-Chongqing region mainly comes from short waves in the westerlies. The short waves in the mid-latitudes were frequent and influenced the region. Due to the joint influence of the southwesterly flows on the western flank of WPSH, and the northerly wind, the Sichuan-Chongqing region forms an area of major water vapor flux convergence. It provides most favorable water vapor conditions for the occurrence of heavy rainfall events. Furthermore, the monsoon air stream, traveling from northern India to the east side of the plateau, arounds the south side of the plateau and transports water vapor eastward, forming another important water vapor channel. The year 2006 is a typical drought year of the Sichuan-Chongqing region, when fewest heavy rainfall events occurred. In this year, the WPSH is easterly, the short-wave trough in mid-latitude westerlies is not active, the southwest monsoon is weaker, and the water vapor convergence in the Sichuan-Chongqing region is less, which are in sharp contrast with 2020.