The invention provides a transformer winding deformation diagnostic method based on discrete wavelet transform. The transformer winding deformation diagnostic method is characterized in that the discrete wavelet transform method is applied to the frequency response analytic diagnosis of transformer winding deformation. The transformer winding deformation diagnostic method comprises performing decomposition process on a measured waveform obtained by virtue of frequency response analysis and a reference waveform at a plurality of layers by virtue of discrete wavelet transform, and then performing mathematical statistical analysis by use of the processed smooth data and diagnosing the deformation degree of a transformer winding according to a corresponding criterion. Such a diagnostic mode is capable of effectively reducing the errors of a traditional diagnostic mode due to white noise interference during frequency response measurement and some local relatively strong interference points and accurately diagnosing the deformation degree of the transformer winding, and therefore, a new judgment method is provided for estimating transformer fault types and the development trend of faults.