The invention relates to a multi-channel rapid corrosion detection and plane imaging diagnosis method for a large grounding grid. The method comprises the following steps of: establishing an originalstructure topological graph of a grounding grid; importing the original structure topological graph of the grounding grid into a computer host; performing optimization and analysis for the original topological graph of the grounding grid by a computer host to obtain an optimal measuring point schematic diagram; performing field measurement of a grounding down lead by a field measurement device; uploading all measured data into the computer host; performing determination of the corrosion degree of the computer host to obtain the corrosion fault degree and the corrosion fault position of the grounding grid; and drawing a grounding grid plane imaging diagnosis topological graph. The optimal measuring point schematic diagram, the corrosion fault degree and the corrosion fault position are obtained through the original structure topological graph of the grounding grid to obtain the plane imaging diagnosis topological graph of the grounding grid, discover the corrosion condition of the grounding grid, make determination and safety estimation for the corrosion condition of the grounding grid and ensure the safe operation and power supply reliability of the power system.