Frequency response analysis is one of the most common methods for diagnosing transformer winding deformation faults. The existing frequency response analysis method has achieved good diagnostic results for a single type of winding deformation faults. However

when the transformer winding has mixed deformation faults

the existing method is less effective in diagnosing the winding deformation. Consequently

we analyzed the characteristics of transformer frequency response curve when mixed deformation faults occurred in transformer windings

and proposed a method based on the fusion of the ratio of the maximum RED to the minimum RED（MMR） and the frequency response curve offset area ratio to diagnose transformer winding deformation faults. The MMR

which has a clear judgment limit for winding axial and radial faults

is used as the determinant for the first fault diagnose layer in this method. In the second fault diagnosis layer

the ratio of shifting area of frequency response curve that is more sensitive to mixed faults is utilized to achieve the purpose of distinguishing single or mixed faults of transformer windings. The simulation results show that

compared with other methods for single fault research

the fusion multi-index method has a better recognition rate when the windings have mixed faults.