During the discharging process of the power transmission system， the electric impulses， the acoustic emission（AE） waves and the relation between them are studied by experiment in laboratory. Based on a large number of experiments the common characteristics of the AE wave of the interior discharge from the insulator， contaminant discharge from the insulator， corona from the transmission line， discharge from bad contact and thunderbolt are summarized， respectively. It is found that the discharge source can be located by means of the phase-shifting between the electric impulse and the acoustic emission wave of the same discharge. The type of discharge can also be identified through the difference in periodicity， the shape and the symmetry of the AE wave of discharge from the power transmission system.