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In this paper, the mal-operation in transformer differential protection caused by magnetizing inrush, the limitations of magnetic flux characteristic principle is first discussed. Then this paper puts forward a new method to distinguish magnetizing inrush based on the ratio of voltage and fluxional differential current. The principle is simple and its implementation is easy. None of the anticipated internal parameters is needed. The advantages of the method are convenient data acquisition, fewer computations and quick operation. The results of simulation testing confirmed that the method is able to clear the internal fault reliably and quickly. Therefore, this method has great practical value.