Abstract: Through the power outage test of the transformer with abnormal state evaluation, several transformer winding deformation defects are found, which provides a diagnostic example for transformer comprehensive state evaluation and abnormal insulation resistance primary judgment winding. Test maintenance personnel first according to the transformer insulation resistance abnormal drop problem, comprehensive analysis of oil chromatography, preliminary diagnosis of its internal winding problem. After that, according to transformer short circuit impedance test, frequency response test and winding capacitance comprehensive analysis, it is inferred that the winding has serious deformation. Combined with the operation of the main transformer over the years and The Times of short-circuit impact, the cause of winding deformation is analyzed comprehensively. Through disassembly analysis, it is found that the transformer windings have different degrees of deformation, which verifies the test and diagnosis results. Through the preventive test, many transformer latent faults are found and avoided in advance, and the comprehensive judgment method of transformer winding deformation is given, which has certain significance for transformer operation and maintenance。