The law of discharge during 220V low voltage line’s contact failure is still unknown, this paper carry out a series of experiments about some factors that may bring about discharge of poor contact. Experimental results the discharge phase region are same no matter that phase line discharge or neutral line discharge, and the phase region are 0°~20°、40°~80°、100°~140°、160°~200°、220°~260°、280°~320°、340°~360°, the law is not change with contact type, gap size, load category and load size.The average discharge of poor contact increases with gap size and contact area when the current increase and it are not less than 25 pC. Finally, analysis of the discharge mechanism of poor contact and factors affecting the poor contact discharge are given by ANSYS software.