It is of great significance to research a method to evaluate the ecological quality status of port sea areas objectively for the ecological environmental protection and sustainable development of sea areas. In this paper, a novel ecological quality status evaluation model is proposed based on the entropy weight method (EW), the gray relational analysis method (GRA), and the TOPSIS method. Firstly, a comprehensive evaluation indicator system is constructed from three aspects, namely seawater quality, sediments, and marine organisms. Secondly, the weight values of different indicators are obtained via the EW method, which can be obtained more objectively than via the subjective weighting method. Afterwards, the ecological quality status of port sea areas can be evaluated using the proposed method, which combines the advantages of the TOPSIS method and the GRA method. Finally, the effectiveness of the proposed EW-GRA-TOPSIS model is illustrated by a case study based on a port sea area of Tianjin. The results show that 66.7% of the monitoring stations in the port sea area are at a good level, 25% of them are at a fair level, only 8.3% are at a poor level, and none are at an excellent or bad level. Additionally, the evaluation results obtained using the proposed model are more consistent with the actual survey results than the compared typical TOPSIS method. It can objectively reflect the ecological quality status of monitoring stations, and consequently, it could be helpful for the marine department to make decisions on the sustainable development of port sea areas. In a further study, the influence of decision makers’ preferences on the evaluation results could be considered, and a more reasonable method to determine the evaluation grade standard should be researched to improve the proposed model.