The present invention discloses a method of manufacturing a metal electrode from seawater to generate electrical energy comprising the steps of: first, using a seawater treatment equipment to heat seawater to 100 DEG C-120 DEG C so as to obtain a concentrated seawater; followed by guiding the concentrated seawater to a precipitation equipment and adding a precipitating agent to obtain a first crystalline material containing magnesium hydroxide; repeatedly heating the first crystalline material to 600 DEG C-1100 DEG C to obtain a second crystalline material comprising magnesium oxide; then feeding the second crystalline material to a separating equipment and adding a reducing agent, and heating to 1200 DEG C-2400 DEG C for generating a metallic magnesium; and finally using the metallic magnesium as a first electrode, performing an electrochemical reaction by supplying electrolyte to the first electrode and a second electrode to thereby generate electrical energy.