The invention relates to a demounting-proof nut and a matched special tool thereof. The demounting-proof nut comprises a retaining nut body with an internal thread and a retaining gland. The retaining nut body and the retaining gland are used in cooperation through balls. The retaining nut body is of an integrated structure formed by connecting a hexagonal body and a cylinder. At least two round through holes are formed in the outer wall of the cylinder of the retaining nut body, and the balls are placed in the through holes. The retaining gland is a ladder sleeve. One end of the inner wall of the retaining gland is a conical face with the outer portion larger than the inner portion. An annular trench is formed in the inner wall of the retaining gland, and the bottom face of the annular trench is in an arc shape matched with the balls. According to the demounting-proof nut and the matched special tool thereof, operation is easy and fast, work efficiency is improved, the labor intensity of workers is lowered, and the fixed asset recycling rate and line construction and maintenance efficiency are improved. The actual work problems of electric transmission line construction and maintenance can be solved.