A simple and efficient electrolysis device for making electrolyzed water from pure water, comprising a controllable electrolysis power supply, an electrolytic electrode plate assembly connected to said power supply, said component being immersed within the to-be-electrolyzed water when in operation. A gap is provided between an anode and a cathode of the electrolytic electrode plate assembly, the gap distance being greater than 0 mm and less than 10 mm, said gap being designed according to the principle of optimal minimization, being less than 0.1 mm when necessary. The area of the surfaces, on either side of the gap, of the anode and the cathode of the electrolytic electrode plate assembly are designed according to the principle of optimal maximization, within the occupied set space. Also disclosed is a simple electrolysis method for making electrolyzed water from pure water.