At the beginning, the ditch was dug for military purposes, and finally the ditch entered the Huaihe River. It is the hub of four major water systems: Jiang, Huai, He and Ji. Not only the transportation hub, but also the Jianghuai area, where Huai 'an was contested. For a long time, Huai 'an has always been a military town that "the south will win and then forge ahead, and the north will win and then pay". However, with the change of history, Hangou has gradually become the main artery of water transportation in the eastern plain of China. At the end of the Eastern Han Dynasty, Han ditch was used for grain transportation. Since then, the economic center has gradually shifted to the southeast, and the water volume in the ditch has been increasing. After the Sui and Tang Dynasties, Hangou was the lifeline to ensure the supply of the imperial court. At that time, water transportation was very difficult, and the water tanker was easy to crash and suffered great losses. Bureaucrats imposed heavy penalties on escorts and boatmen. At that time, it was stipulated that Cao rice was transported from Jiangnan to Chang' an, and one tenth of the loss was a capital crime, but more than half of it was lost. In the year of famine, hungry people dug up leftover rice in the Caohe River to satisfy their hunger. It can be seen that the loss of Caomi was not simply stolen for the escort. During the Northern Song Dynasty, the grain from Jianghuai to Bianjing amounted to 8 million stones a year, not less than 6 million stones, which was the most important transportation channel at that time. During the Ming and Qing dynasties, the position of valley water transport was more important. During the grain transportation season, there are1.20,000 water transport vessels and120,000 water transport troops "sailing for several provinces". Since then, an important town, Beichen Town, has quickly appeared at the end of the Hangou estuary. After the development of Qin, Han, Wei, Jin, Southern and Northern Dynasties, Beichen Town flourished rapidly and became Chuzhou Prefecture in Sui and Tang Dynasties. With the north-south connection of the Grand Canal, it has become a major waterway transportation and Tianjin, and its commerce and trade are very prosperous, attracting businessmen at home and abroad. Bai Juyi praised this place as "the first state in the southeast of Huaishui".