The initial faults inside transformer would eventually develop into catastrophic failure during its operation, which could result in the outage of equipment and entire network. Winding deformation is considered to be the most common faults inside transformer. As power transformer is under the impact of overvoltage during its operation, the method of transient overvoltage could be used to realize online detecting transformer winding deformation is proposed in this paper. Firstly, the basic principle of this method is developed, then a verifying test platform is set up, and the simulation test of shorted turns failure is completed. The test result shows that the proposed method could realize detecting shorted turns failures of transformer winding to a certain extent, and this method has a certain reference value. .