With the energy saving and emission reduction policies, it is urgent to guide the port industry towards decarbonization through the establishment of an evaluation system and methodology for port competitiveness under this “dual carbon” target. This paper establishes a methodology consisting of Entropy Evaluation, Grey Relational Analysis, and TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) for ranking port competitiveness under the “dual-carbon” goal. Specifically, the port competitiveness indicator candidates are chosen from 25 indicators, which are specific ones generated from five first-level indicators of “port service level, port facilities and equipment, port resource consumption, port pollutant emission, port development potential”. The quantitative and qualitative indicators are utilized during the selection to calculate the Gini coefficient and the measurability analysis. Data from 10 major ports in China in 2022 validate this methodology and the procedure.