The invention discloses a transformer oil sludge ageing composition detection method which comprises the following steps of step 1, mixing aged oil sludge with a solvent, heating a mixture, and performing separation to obtain clear liquid and filter residues; step 2, detecting elements and contents thereof in the clear liquid in the step 1, and detecting elements, contents thereof, iron oxide, a crystalline compound, fiber substances and X wax in the filter residues in the step 1; and step 3, comparing the elements in the clear liquid and the elements in the filter residues obtained in the step 2 to elements in new transformer oil or aviation kerosene, and judging a source of an oil sludge ageing product. By judging the elements in the clear liquid and the filter residues in the transformer oil sludge as well as the iron oxide, the crystalline compound, the fiber substances and the X wax in the filter residues, the transformer oil sludge ageing composition detection method accurately and rapidly diagnose the oil sludge ageing composition and the source thereof comprehensively and meets the requirement for rapidly diagnosing the oil sludge ageing product.