The overall strength of economic about hinterland of the port is determined by Relative gravity coefficient model,based on which Granger test and dynamic analysis of VAR are performed on the three ports-Shanghai port,Shenzhen port,and Guangzhou port,and then get the following conclusions:Firstly,Shanghai port and Shenzhen port are Granger cause for their hinterlands,while the hinterlands are not the Granger cause for the ports.The situation of Guangzhou port is the opposite.Secondly,Guangzhou port and its hinterland have a positive impact on each other,but the impact of Guangzhou port on its hinterland is not obvious.Thirdly,Shenzhen port has a biggest positive impact on its hinterland.Fourth,Shanghai port's hinterland has a positive impact on it sometimes and a negative impact at the other times,while it has a moderate positive impact on its hinterland.