Abstract: For the purpose to identify the sources of groundwater and salt and the salinization of shallow groundwater in the coastal area of Yancheng, Jiangsu province, different types of water samples are collected, such as the river water, rainwater, seawater, underground fresh water, brackish water, salt water in the study area during the period from 2018 to 2019. The chemical composition and ions ratio, Piper diagram, hydrogen and oxygen isotopic composition and ¹⁴C dating results are analyzed. The results suggest that: (1) The phreatic water and the first confined water are dominated by saline water. The upper layer of the phreatic aquifer is less than 10 m in thickness and widely desalinated, which changes seawards from fresh water, brackish water to salty water. (2) The water in the phreatic aquifer and the first confined aquifer mainly come from precipitation replenishment in the Holocene warm period, and salinity mainly come from the ancient residual seawater that has suffered strong evaporation and concentration. (3) Groundwater in the phreatic desalination layer mainly comes from modern precipitation replenishment, and salinity mainly comes from the dissolution of rock salt and aluminosilicate minerals, the salinization of groundwater in some areas of the abandoned Yellow River estuary is mainly affected by seawater intrusion.