Abstract: Frequency response analysis is the main method for measuring transformer winding deformation at present. Based on an incident of mismeasuring transformer winding deformation due to inadequate application of frequency response analysis, this paper analyzes the causes of mismeasuring transformer winding deformation from the basic principle and practical application of frequency response analysis, and summarizes and analyzes the factors that need to be considered for comprehensive analysis of on-site test data. The points that should be paid attention to when using frequency response analysis method in transformer winding deformation experiment are put forward to avoid similar events from happening again.