Abstract: Based on observed precipitation data, radar data and NCEP 6 h interval reanalysis data with 1°×1° resolution, we analyze the heavy rainfall event in Chongqing from September 17th to September 19th, 2014. The results are as follows. (1) The circulation background of that heavy rainfall maintains the "two troughs and one ridge" situation in mid-latitudes. The plateau trough moves eastward to the middle and eastern part of the Sichuan Basin to cause cold air behind the trough flowing southward and affecting Southwestern China. The tropical cyclone "Seagull" transports warm air and instability from South China Sea to the heavy rainfall region, together with water vapor from the bay of Bengal. (2) Typhoon "Seagull" weakened and evolved into a shear line. The tropical depression "Phoenix" strengthens and presses subtropical anticyclone, which makes subtropical anticyclone stable in motion and meridional circulation increases. The typhoon "Seagull" interact with typhoon "Phoenix" that transport the warm and humid air and unstable energy of South China Sea and the bay of Bengal to the precipitation area together. (3) The entire layer of the precipitation area is controlled by warm advection at the beginning of the heavy rainfall, while weak cold flow appears and gradually intensifies in the lower troposphere as the cold air behind the trough pours into the area. (4) The cold air from the north pouring into the lower layer converges with the warm and wet air from the South, resulting in an energy front tilting northwest, and the warm and wet air climbs along the energy front with the cold air spreading south, leading to enhanced ascending motion in the precipitation area to increase rainfall.