The invention discloses a waveform visualization based same-period loop polarity detection apparatus and detection method. The apparatus comprises an oscilloscope and a same-size ratio isolation transformer, wherein the same-size ratio isolation transformer comprises an isolation transformer A end, an isolation transformer B end, an isolation transformer C end and an isolation transformer D end. The isolation transformer A end and the isolation transformer B end are homonymous input ends at the primary winding side and the secondary winding side of an isolation transformer; and the oscilloscope is provided with a set voltage input end and a system voltage input end. According to the invention, the waveform visualization based same-period loop polarity detection apparatus can carry out a phase checking test on the secondary side of a voltage transformer and facilitates integrated analysis of waveforms and correlation test conditions after the test; and the apparatus finishes processing and analyzing of the voltage quantity, the current quantity and the switching quantity, which are acquired, of each side of a same-period loop. The oscilloscope has waveform storage and auxiliary analysis functions, meets an onsite waveform analysis need and can realize an external printing function.