The transport and diffusion of warm discharge water from the power plants near Shidongkou in the Changjiang Estuary were analyzed based on the observation data from November 23 to December 2 in 2014. During the spring tide, in terms of the longitudinal distribution of water temperature, warm discharge water from the power plants was evident, and had the maximum water temperature rise of 4.1oC in ebb tide, and of 5.1oC in flood tide; water temperature was stratification only near the discharge port, and trended to vertical uniform in other area due to strong mixing induced by tidal current. In terms of horizontal distribution of water temperature and water temperature rise, water temperature was higher along the coast and lower away from the coast, and reached the maximum value of 4.0oC near the discharge ports of Huaneng Shidongkou power plants during the ebb tide. The warm discharge water was transported and diffused downstream along the coast forced by the ebb current and Coriolis force. Compared during ebb tide, the higher temperature water near the Shidongkou move upstream and farer away the coast during flood tide, the maximum water temperature rise reached to 4.2oC. In terms of current speed and direction, water temperature measured at the continuous sites, water temperature rise during flood tide if the measured sites located in the upper reaches of the power plant, and descend during ebb tide if the measured sites located in the lower reaches of the power plant, was influenced distinctly by the near warm discharge water from the power plants. The more the measured site closer to discharge port of power plant, the higher the water temperature was, and the more obvious the vertical variation was. During the neap tide, water temperature was lower than during spring tide due to the passage of the cold front and heat loss at the river surface, the maximum water temperature near the power plant appeared at the middle water layer. The distribution characteristic of warm water rise was similar to the one during spring tide. The maximum warm water rise reached to 5.0oC which was higher 0.8oC than the one during spring tide because the tidal current and mixing was weaker during neap tide, and the higher temperature water near the warm water discharge port was not easy to be outward transport and diffusion.