A spectrometric transformer oil detector comprises a spectrograph host machine and an impurity filtration device, wherein the impurity filtration device comprises a support, two volume measuring instruments and a filter are installed on the support, the two volume measuring instruments are respectively installed at the upper portion and the lower portion of the filter, and the volume measuring instruments are in serial connection with the filter. A second communication pipe is arranged between the impurity filtration device and the spectrograph host machine, and a delivery pump is arranged on the second communication pipe. Detected transformer oil can be filtered before detection, insoluble sludge, fiber and dirt are filtered out, and spectrograph blockage is avoided. The volume of impurities can be calculated after filtration through the impurity filtration device to determine whether the detected transformer oil can be used again or not after undergoing filtration processing, accordingly it is determined whether transformer oil change is necessary or not, and waste is avoided. After the filtered transformer oil undergoes detection of a spectrograph, the influence of solid matter can be reduced, physical factors can be eliminated, and an obtained experimental result is more appropriate to production and use.