The invention relates to a power transformer load tap changer switching contact burning fault diagnosis method and device thereof; wherein the diagnosis method includes determining an area higher in vibration signal energy, finding a center point high in energy in a switching moment, avoiding an area possible to influence analysis; selecting a signal to be analyzed, calculating energy of the signal according to energy calculation formula (1), and determining that whether the load tap changer switching contact is in burning fault. The diagnosis device is in the structure that the transformer tap changer is connected with a sensor, the sensor is connected with a signal conditioner, the signal conditioner is connected with a capturing instrument, and the capturing instrument is connected with a microcomputer. The invention has the advantages that: the found fault characteristic value can accurately reflect tap changer switching contact burning fault, characteristic is obvious, repeatability is good, and the method has universality on tap changers of the same type; fault diagnosis technology is simple in engineering realization, and the sensor is convenient in installation; and a microcomputer is adopted for detection, processing and diagnosis, performance is reliable, and diagnosis conclusion is visual.