The invention discloses a microarc oxidation surface treatment method for treating a large-area light alloy and a corresponding device for implementing the method. The method includes the following steps: arranging a cathodal electrode device with a surface area smaller than the surface area of an anodic workpiece on a local area of a large-area anodic workpiece, so as to process microarc oxidation surface treatment to the local areas of the anodic workpiece; and adjusting the position of the cathodal electrode device relative to the anodic workpiece and gradually enabling the cathodal electrode device to have reaction with all the areas on the surface of the anodic workpiece. All the areas have the same degree of reaction, so the whole surface of the anodic workpiece can be processed with microarc oxidation treatment. The technical proposal is adopted to have the advantage that when processing microarc oxidation surface treatment to different areas of the large-area light alloy, the position of the relative electrode with respect to the anodic workpiece can be adjusted freely. The device is convenient to install and disassemble. The invention has wide application range and can save energy and reduce cost, thus effectively reducing the production cost.