Disclosed is a disassembling tool for an oil cup of a transformer breather. The disassembling tool comprises a tool body and a handle. A locating surface is arranged on the inner side of the tool body, the handle is arranged on the outer side of the tool body, and a locating part is arranged on the tool body. The locating part is located in an air guide hole formed in a metal connecting piece, the disassembling tool is rotated in the clockwise direction through the handle, the disassembling tool is rotated independently at first until the locating surface abuts against the outer side wall of the oil cup, then the metal connecting piece is driven by the disassembling tool to rotate, and is loose through rotation, and the oil cup is taken down; otherwise, the metal connecting piece is rotated in the anticlockwise direction, and the oil cup is installed. Assembly and disassembly of the oil cup are convenient, the assembling and disassembling time is saved, the efficiency is improved, and the damage to the metal connecting piece and the oil cup cannot be caused.