Based on the Environmental Fluid Dynamic Code (EFDC), a 3-D water temperature and salinity model for the Changjiang Estuary and its adjacent areas was established. River discharge, tide, wind and solar radiation were considered in this model. Compared with the observed data in July 2005, the simulated results were fairly consistent with the observations. It can be analyzed from the results that the temperature isolines off the Changjiang Estuary in summer are along the south-north direction, with high values nearshore and low values offshore; in the Changjiang Estuary, the temperature is descending from the estuary to the offshore along the direction of Changjiang Diluted Water (CDW). The characteristics of CDW are prominent in summer. The low-salinity surface water can reach out 123° E and has a trend of east expansion off the Changjiang Estuary. The intensities of themocline and halocline are extremely high at the area of CDW, which reach the values of 0.3 ℃/m and 2/m, respectively. The positions of thermocline and halocline are coincident or close-by off the Changjiang Estuary.