On the basis of adjusting the openness of maritime transport service trade which is calculated by traditional method and the panel data of 26 maritime countries, 2001~2012, this article does an empirical study on the relationship between the openness and competitiveness of maritime transport service trade with the dynamic panel GMM estimation method. The result shows: the openness and competitiveness of maritime transport service trade is not a simple linear relationship, but presents an inverted U relationship. During the initial period of the process of maritime transport service trade liberalization, a country’s competitiveness of maritime transport service trade will be enhanced along with the greater openness. However, when the openness surpasses a certain level, it will have a negative effect on the competitiveness. Therefore, under the guidance of moderate market opening principle of maritime transport service trade, China should enhance the support and protection to maritime transport service trade corporations, and promote their competitiveness in improving the innovation of corporation management.