In recent years, ports in China have increasingly become one of the ideal investment locations for international capital. The analysis of the relationship between foreign direct investment and market structure of ports in China has a certain reference value for the further study of the development of port market structure. It also helps to make proper port policies for our government. In this paper, we take port group of the Pearl River Delta for instance. Two independent variables, the whole amount of foreign direct investment and enterprises number, are selected in the regression model to test the relationship between FDI and market concentration, which is based on the calculating of related coefficient between them. It is concluded that FDI promotes the concentration of port markets to some extent, aggravating port market monopoly.