The invention discloses a sound-speed-based method for identifying the material of a transformer winding. The method specifically includes the following steps that S1, audible sound waves are generated at the head end of the transformer winding through a vibration exciter; S2, sound sensors installed at the head end and the tail end of the transformer winding receive sound wave signals; S3, the signals collected by the sound sensors are introduced into an oscilloscope, wherein the time difference between the head waves of two waveforms is sound wave transmission time; the sound wave transmission speed is calculated through the formula v=L/t, wherein v is the sound speed, L is the sound wave transmission distance, and t is the sound wave transmission time; S4, the material of the transformer winding are identified according to the calculated sound wave transmission speed and known sound wave transmission speeds. By means of the method, under the condition that winding insulation is not damaged, whether the material of the transformer winding is copper or not can be easily and rapidly identified.