The invention discloses a grounding mode self-recognition power distribution network line differential protection device. The device comprises a collecting circuit, a calculating circuit, a judging circuit and a zero-sequence differential protection circuit, wherein the collecting circuit is used for collecting the electric quantity characteristics of a current power distribution network line respectively, wherein the electric quantity characteristics comprise zero-sequence voltage, own-side zero-sequence current and opposite-side zero-sequence current; the calculating circuit is used for calculating the zero-sequence differential current of the current power distribution network line; the judging circuit is used for judging whether the grounding mode is a neutral low-resistance grounding mode; the zero-sequence differential protection circuit is used for starting zero-sequence differential protection and outputting a control signal so as to control the switching-on and switching-off of the switch of the current power distribution network line when the grounding mode of the current power distribution network line is the neutral low-resistance grounding mode. The invention also discloses a grounding mode self-recognition power distribution network line differential protection method. The grounding mode self-recognition power distribution network line differential protection device provided by the invention solves the problem that the power distribution network line cannot be protected when the grounding mode changes.