Salinity gradient energy (SGE) exists in solutions with different salinity, such as seawater and freshwater. However, recovery of this energy between concentrated seawater discharged from desalination plants and seawater is rarely studied. Here, the reverse electrodialysis (RED) approach is proposed to capture this energy for power production. The main works are: i) Investigating influence law of feed parameters on the performances of a RED stack. ii) Exploring the influences of the sediments in concentrated seawater, produced in thermal desalination process, on performances of the stack. When seawater is used as dilute solution, open-circuit voltage of the RED stack increases 2.39 times from 0.132 V to 0.448 V with concentration of concentrated seawater increasing from 1.0 mol L−1 to 3.0 mol L−1, and the maximum power density increases from 0.0120 W m−2 to 0.184 W m−2. Increasing the temperature and velocity of feed solution can improve the performance of the RED stack, but with the limitation of concentration difference. The sediments in concentrated seawater are harmful to output performances of the RED stack. After filtrating most sediments, the maximum power density increases 19%, and open-circuit voltage increases 9.4%, compare to their original values.