Analysis of the rainstorm on 22 June 2015 in Nanchang was carried out using conventional observations. Backward trajectories up to 240 h were simulated and studied based on the HYSPLIT model and the NCEP 6 h 1°×1° reanalysis data. Cluster analysis of mid-low level trajectories was performed to analyze the change of moisture content of air parcels. The results showed that (1) the rainstorm developed ahead of the 500 hPa trough and the northwestern periphery of subtropical high. Tropical cyclone “Kujira” in the South China Sea also induced low-pressure systems, shear lines, low-level jets in the mid-low levels and divergence at 200 hPa. The rainstorm was located near a cold front with little potential instability and weak vertical wind shear. (2) In general, six major paths of moisture transport were found by clustering. Water vapor mainly came from the western part of Western North Pacific (46.7% of 180 backward trajectories) above 1500 m, followed by the eastern part of the South China Sea (24.4%) below 3000 m. 11.7% of the trajectories were originated from the east of the Bay of Bengal, the south of Indochina Peninsula and the south of Yunnan Province of China, and the remaining three clusters constituted less than 9%. (3) Air parcels from the two major clusters were observed to have higher moisture content as they were close to the surface over their maritime origins, which made the air parcels still have high specific humidity and relative humidity when they reached Nanchang, thus contributing greatly to the rainstorm. Air parcel that ended up in Nanchang over 3000 m and came from the Western North Pacific was originally dry in nature, but it became much more humid after it subsided and picked up moisture. With steady subtropical high and a tropical cyclone in the South China Sea just south of the subtropical high, moisture brought along by the easterlies or southeasterlies at the periphery of the high was an essential ingredient of rainstorms in the northern part of Jiangnan Region.