The invention relates to a corrosion method for displaying grain boundaries of high-damping manganese-based copper alloys. Metallographic corrosion is carried out for high-damping manganese-based copper alloys whose Mn content is higher than 70% and Cu content is higher than 20%, and a sample is prepared according to a conventional method; a saturated solution of picric acid and a nitric acid alcohol solution whose concentration is 5-15% are fully mixed according to a volume fraction ratio of 1 to 0.8-1 to 1.2, and the solutions are placed at a normal temperature for at least 10 minutes; a polishing surface of a sample is upward and placed in a corrosive agent, corrosion is carried out for at least 4 minutes, the corroded high-damping manganese-based copper alloy sample is taken out and washed with flowing water as well as washed with alcohol and dried, and etching is completed for displaying crystal boundaries; observation is carried out under a 100x microscope in order to obtain crystal grain displaying photographs, and a comparsion method or a grid method or a resection is used for carrying out determination of grains. The corrosive agent is used for corroding in order to obtain clear grain sizes, corrosion of matrix structures is avoided, and the problem that crystal boundary and twin crystal appear at the same time is solved; and the method has the advantages of simple operation, accurate determination, higher accuracy, and usage safety.