Since the reign of Emperor Yongle(永乐), the water transport system based on "Yuan transport"(远运, long distance, great amount and huge cost of transportation) gradually replaced the civil transportation system of Hongwu(洪武) period, which initiated the process of reforming tribute grain transport system from Zhi transport(支运)to Dui transport(兑运)in the Ming Dynasty. From the "three methods of grain transport"(sea transportation, river and land transportation and Dezhou warehouse transportation) to "three major reforms of tribute grain transport system"(Zhi, the combination of Zhi and Dui, Dui), the pattern of civil-military combined transport has been mixed with more economic factors. Therefore, grain transport was no longer simply a matter of labor service. The implementation of Gaidui(改兑, direct transportation) method was the symbol for the formation of "all grain is transported by the army" in theory. However, the civil transport never completely vanished. The essence of the "three major reforms of tribute grain transport system" lies in the fact that the army has become the main body of grain transportation.