Abstract: Based on the relevant data of 13 coastal port cities in eastern China from 2000 to 2021, the coordination degree model and panel threshold model are constructed to explore the coordinated development of port-city environment and its impact on urban economic competitiveness. The research results show that: 1) In terms of the degree of coordination between port and city environments, most ports in the eastern region and their hinterland cities are at the stage of moderate or serious imbalance. On the whole, the degree of port and city environmental coordinated development needs to be further improved. 2) The coordination degree between port and city environment has a significant impact on urban economic competitiveness, and this impact slightly weakens with the development of port and urban economy; among the influencing variables of coordination degree, fixed asset investment and foreign trade are significant factors to enhance urban economic competitiveness. 3) At present, there is a "U-shaped" relationship between port-city environmental coordination degree and urban economic competitiveness. The environmental coordination relationship of coastal port cities is on the right side of the inflection point of the "U-shaped" curve. Therefore, adhering to the concept of giving priority to ecological development, expanding investment in fixed assets and actively developing foreign trade are conducive to the competitiveness of urban economy in coastal port cities.