A device and a method for preparing pure titanium by electrolysis-chlorination-electrolysis, wherein the device includes a first electrolytic cell, a second electrolytic cell, a chlorination reactor and guide tubes. The Cl2 generated at the anode of the first electrolytic cell is introduced into a chlorination reactor containing the TiCxOy or TiCxOyNz raw materials via a guide tube, and a chlorination is carried out to generate TiCl4 gas at a temperature of 200° C.-600° C. The TiCl4 gas passes through a guide tube into a cathode of the second electrolytic cell, and then an electrolysis is performed to obtain the high-purity titanium in the second electrolytic cell. At the same time, the Cl2 generated at the anode of the second electrolytic cell is recycled into the chlorination reactor in the first electrolytic cell to continue to participate in the chlorination of TiCxOy or TiCxOyNz.