Using the spatial equilibrium model, this study estimates the flow direction and quantity in thirty-one provinces and three overseas imported strongholds, including Dalian, Ningbo and Fangchenggang, and it reveals Dalian as a representative port city plays an important role in the process of grain transshipment at home and abroad. Lastly, this paper puts forward the key to future development lies in the center position of the key port city as the grain logistics and the fixation of the function of each port city.