The present invention discloses a grounding mode automatic identification-based power distribution network feeder line and supply line protection device. The device comprises an acquisition circuit, a judgment circuit and a zero sequence over-current protection circuit; the acquisition circuit is used for acquiring the electrical quantity characteristics of a present line, wherein the electrical quantity characteristics comprise present zero sequence current and present zero sequence voltage; the judgment circuit is used for judging whether the grounding mode of the present line is a grounding mode according to which a neutral point is grounded through a small resistor according to the electrical quantity characteristics of the present line; and the zero sequence over-current protection circuit is used for enabling zero sequence over-current protection when the grounding mode of the present line is the grounding mode according to which the neutral point is grounded through the small resistor, and outputting control signals to control the on-off of the switch of the present line. The invention also discloses a grounding mode identification-based power distribution network feeder line and supply line protection method. With the grounding mode automatic identification-based power distribution network feeder line and supply line protection device provided by the invention adopted, the problem that a power distribution network feeder line and supply line cannot be protected when a grounding mode is changed can be solved.