In order to deeply analyze the scale distribution and evolution process of the port group in the Yangtze River Delta，we apply cargo throughput and container throughput as the indicators to measure port scale，and use the port primacy index and the rank-size rule to study the port scale distribution in the Yangtze River Delta. The results show that the gap of ports in the Yangtze River Delta has been narrowing，and the port scale distribution has evolved from the primacy distribution to the rank-size distribution. The port scale structure of Jiangsu Province is relatively loose and the combined effect of high-ranking ports is not obvious，while the distribution of port throughput in Zhejiang Province is too concentrated. The scale distribution of the port group in the Yangtze River Delta is generally decentralized. In the future，it is necessary to accelerate the development of small ports such as inland river port and further optimize the port system structure. The port clusters in the Yangtze River Delta has formed a relatively stable and decentralized cargo transportation system，while container transportation is developing rapidly with new container ports keep emerging. The hierarchical system is still in constant change. The scale distribution of container port in the Yangtze River Delta has a higher degree of concentration.