Canal water transportation is often due to drought and shallow water, and the river is blocked, which leads to the failure of tankers to arrive on schedule. In order to overcome the difficulties of water transportation and the shortage of water transportation subsidies, the rulers of the Yuan Dynasty paid more attention to another trunk line of water transportation-sea lanes. In the 19th year of Yuan Dynasty (1282), the Yuan government ordered Robbie, Zhu Qing, Zhang Xuan and others to supervise the construction of 60 seagoing ships, recruited Cao Ding and Cao Fu, and opened up maritime transportation. Zhu Qing and Zhang Xuan are pirates. They used to ship books collected in the Song Dynasty to zhi gu for the Yuan Dynasty and were familiar with the sea route between Shanghai and Tianjin. Most of the Cao Ding Cao Fu they recruited were also familiar with shipping. In order to encourage their enthusiasm, the Yuan government distributed rations to five people in each household. In this way, the maritime water transport increased year by year, from 46,000 stones in the 19th year of Zhiyuan to1590,000 stones in the 27th year. From Yuan Wuzong to sophomore (1309), it increased to 2.46 million stones; In the second year of Yuan Wenzong calendar (1329), it increased to 3.2 million stones.

After the implementation of grain transportation, it facilitated the northern transportation of grain in Jiangnan area; When the tanker returns, it carries beans, grains and local products (pears, dates, etc.). ) spread from the north to the south, which promoted the material exchange between the north and the south at that time. However, at that time, because we could not effectively grasp the changes of marine climate and were not familiar with the situation of maritime routes, maritime transportation was very difficult and dangerous. Under the attack of wind, fog and pirates, a large number of Cao Ding and Cao Fu are buried at the bottom of the sea every year, and a large number of grain carriers sink; The loss of grain is above1100,000 stone per year on average.

In order to find an economical and safe shipping route, the waterway transportation route was changed three times in the twelve years from 19th to 30th of Yuan Dynasty (128- 1293). The third route is: Sansha, from Liujiagang (now Liuhe, Taicang County, Jiangsu Province) to Chongming Island, entering the deep sea, going north through Chengshanjiao to northwest, passing through Liujiadao and Shamen Island, passing through Laizhou Bay, and reaching Haikou, zhi gu. This new route is shorter and faster than before, and it can be reached in ten days when the wind is good.

In addition, in order to overcome the difficulties of maritime transportation, the maritime authorities of the Yuan Dynasty accepted Su Xian's suggestion in the fourth year (13 1 1) and set up a beacon ship in Xishan Shazui to direct ships entering and leaving the Yangtze River estuary. In the first year of Yanyou (13 14), he accepted Yuan Yuan's suggestion and set up flags at nine places in Jiangyin, such as Xiagang and Xugou, to guide ships. In December of the fourth year of Yanyou (13 17), a mound was built in front of Longshan Temple, and there were stones around the mound. On the mound, from April 15 every year (Spring Festival travel rush will start on April 15), the beams will be hung high during the day and lights will be hung at night to direct the ships. This has achieved good results.