The invention discloses an impedance circle characteristic-based transformer winding deformation discrimination method. According to the method, voltage and current information of the primary and secondary sides of a transformer is utilized to draw a relation graph of voltage drop and primary-side current, and the two-dimensional graph is an ellipse and is called an impedance circle of the transformer; under a normal condition and a diagnosis condition, based on the change of the shape of the impedance circle, characteristic quantity, namely, eccentricity ratio which indicates the change of the ellipse, is utilized to judge whether the structure and position of windings are deformed and the severity of deformation, and therefore, measures can be taken, and corresponding operations such as early warning, maintenance and operation exiting can be adopted for the transformer, and the safe and stable operation of the transformer can be ensured.