Abstract: In view of problem that correctness of protection polarity cannot be determined since new power plant cannot provide enough load to general test instrument, the paper proposed a new method of applying waveform record of starting load to analyze protection polarity. The method uses time relation of waveform record to deduce angle relation of electric variables, namely converting time difference calibrated by waveform record of peak of voltage and current to phase angle, so as to judge correctness of protection polarity. The test result showed that the method is simple and practical.