The invention relates to a transformer polarity testing system, which comprises a battery box, a transformer under test and a polarity tester, and is characterized in that the primary side of the transformer under test is connected with the battery box; the secondary side of the transformer under test is connected with the polarity tester; the polarity tester comprises a polarity indicator and a polarity testing system circuit; and the polarity indictor is connected in the polarity testing system circuit. The transformer polarity testing system designed according to the invention can be operated by a single person or multiple persons, has a delayed reset function and can maintain a test result; the instrument has a logic function and can effectively recognize the polarity of the transformer; the polarity of the transformer can be quickly judged by an operator by the means such as sound, light and fixed deflection of a pointer so as to form effective monitoring; and a photoelectric coupler is enabled to creatively act as a sensor of transformer polarity testing, and the efficiency of transformer polarity testing is significantly improved.