To quantitatively analyze the relationship between ports and cities in the Yangtze River Delta and its changing laws，this study takes cargo throughput and urban GDP as measurement indicators and investigates the relationship with the dynamic relative concentration index. The results reveal that 1）the port-city relationships of the 14 port cities in the Yangtze River Delta can be divided into port-driven，port-city coordinated，and city-driven ones，and the changing trends can be categorized as rising，falling，and fluctuating. 2）The development of ports in the Yangtze River Delta is relatively mature in general. In the past 15 years，the port-city relationship has changed from port-driven development to port-city coordinated development，and urban development is relatively more active. 3）The port activity of Lianyungang continues to decline. External factors such as the deep-water channel of the Yangtze River and inland water shipping have brought new development opportunities to ports such as Zhenjiang，Taizhou，and Jiaxing. In the port-city relationships driven by cities such as Shanghai and Nanjing，the active factors of the ports are reduced，and the urban growth effect is far greater than that of the ports.