The invention discloses a method for determining single lightning stroke protection effectiveness of an overhead line insulator parallel gap. Currently a method for determining whether an single lightning stroke event parallel gap performs effective protection on an insulator is a manual tower climbing line inspection manner, thereby searching whether a lightning burning trace exists on the surface of the insulator. The method has defects of relatively high manpower consumption and low efficiency. According to the method of the invention, a lightning current amplitude of a single lightning stroke event is acquired through a lightning positioning system, and furthermore a lightning impact voltage threshold which is bear by the insulator and the parallel gap is calculated. According to a protection effectiveness rule of the parallel gap in different lightning impact voltage thresholds, whether protection of the parallel gap to a disc type suspended insulator in the lightning stroke event is effective is determined. According to the method of the invention, protection effectiveness of the parallel gap is determined according to calculation, thereby realizing no manpower consumption and higher efficiency.