The present invention relates to an electrochemical method for continuously producing a pure-oxygen gas and an oxygen-lean gas from an oxygen-containing gas mixture. At least two water electrolyzer units and two power supply units are used, of which each former solely corresponds to each latter, respectively. The two power supply units are at least one power supply unit of recycling hydrogen energy and an externally-connected power supply unit. The power supply unit of recycling hydrogen energy consists of hydrogen fuel cells, and the externally-connected power supply unit is comprised of at least one of the following cells and/or power supply, e.g. (a) solar cell(s), (a) direct methanol fuel cell(s), and/or an AC grid. In terms of the electrical circuit, each power supply unit is solely connected with the corresponding water electrolyzer unit. Hydrogen produced by all the water electrolyzer units is delivered to feed the hydrogen fuel cells as a fuel, and oxygen produced by the water electrolyzer units is the pure oxygen of target product. A negative electrode and a positive electrode of the hydrogen fuel cells of the power supply unit of recycling hydrogen energy are fed by the hydrogen gas and an oxygen-containing gas mixture, respectively. The inlet hydrogen gas is connected with a cathode of hydrogen chamber of the water electrolyzer unit through a pipe. A gas-liquid separation is performed at the outlet of positive electrode, of which the outlet gas is produced as an oxygen-lean gas. By means of the present invention, a high-purity oxygen gas can be stably and continuously produced from air at low cost for any indoor and outdoor sites or a remote area.