Abstract: DC resistance test is an indispensable test item in the factory, handover, overhaul, and pre-test test of power transformers. When the power transformer break down, we can check the overall connection of the power transformer windings and the quality of the wire by DC resistance test. This paper summarizes the common failuere causes of nnbalanced DC resistance. By analyzing the date performance of unbalanced DC resistance in the cases, the fault locations of the transformer have been diagnosed, whice provides maintenance basis and direction for transformer maintenance, and accumulates experience for improving transformer maintenance quality.