The invention discloses a winding state evaluation method in the condition of a transformer external fault. According to the method, current flows through a transformer winding conducting wire, the magnitude of the electromagnetic force is proportional to the square of passing current, in the condition of high fault current, the electromagnetic force born by a winding is hundred times of that in a normal condition, winding formation happens when winding strength is insufficient, elastic deformation is partly recovered after fault elimination, however the cumulative effect of the winding deformation causes a large accident in the next fault condition. According to the method, the collected current data of two sides of a transformer before and in the fault is used, an appropriate numerical algorithm is utilized, the values of leakage inductance of the transformer before and in the fault are identified and obtained, the deviation of winding leakage inductance in each time in the fault is calculated and analyzed, the tendency chart of the deviation is made with time as a horizontal ordinate, and the shock to the transformer winding by the fault and the state of the winding are evaluated according to the deviation tendency chart.