Since ancient times, due to the barrier of the natural moat of the Yangtze River, the traffic between the north and the south of the Yangtze River is inconvenient, so the Yangtze River has become the dividing line for regional division. Geographically, the earth rotates from west to east, and the Yangtze River in the northern hemisphere will be subjected to geostrophic deflection to the right (in line with the right-hand law). Generally speaking, the Yangtze River flows from west to east, scouring the south bank, causing sediment accumulation on the south bank, and the terrain is flatter than that on the north bank. It has promoted the formation and development of the population of agricultural economic cities on the south bank. At the same time, the south bank is seriously eroded, which makes the waterline of the south bank of the Yangtze River deeper. Therefore, some large and medium-sized ports, such as Wuhan Port, Nanjing Port and Shanghai Port, are mostly located on the south bank of the Yangtze River. Since the Ming and Qing dynasties, especially from the Republic of China to modern times, most of the trade of some businessmen has gathered in Jiangnan. The south bank is rich in water, and the climate in the south of the Yangtze River is generally warmer and wetter than that in the north of the Yangtze River, so the agricultural output in the south of the Yangtze River also greatly exceeds that in the north of the Yangtze River, which makes the economy in the south of the Yangtze River more developed than that in the north of the Yangtze River. Moreover, due to the natural barrier of the Yangtze River, it is difficult for the civil war to spread to the south of the Yangtze River. With the influx of more people, other industries have also developed, and the industrial structure is easier to improve. For a long time, it has caused the development difference between the two sides of the Yangtze River, making it easier for Jiangnan to become a regional political, economic and cultural center. Of course, with the development of transportation and economy, the Yangtze River is no longer an obstacle to economic integration in many places, and the gap between Jiangnan and Jiangbei is gradually narrowing. Many cities put forward cross-river development, and Jiangbei gradually merged into one.