The invention discloses an electrochemical reactor, a method for removing chlorine ions in waste water through electric flocculation, a precipitation product and an application. The electrochemical reactor comprises one or more reaction tanks, wherein an anode and a cathode in the reaction tank alternately arranged; the anode is a copper electrode; and the cathode is an inert electrode. The method comprises the steps of introducing to-be-treated waste water into the reaction tanks of the electrochemical reactor and immersing the anode and the cathode into the waste water; applying constant current between the anode and the cathode and lastingly stirring the waste water. According to the invention, an agent does not need to be additionally added, the possibility of secondary pollution is very low, the reaction conditions are mild and limitation of the concentration range of the chlorine ions is avoided. Meanwhile, the device used for reaction is simple, relatively low in cost and beneficial to automation.