The invention discloses a distribution network bus protection device with a grounding mode automatic identification function. The device comprises a collection circuit, a judgment circuit, and a zero sequence differential protection circuit. The collection circuit is used for collecting the electrical characteristics of a current bus line, wherein the electrical characteristics includes the zero sequence differential current of the current bus and the zero sequence voltage of the current bus. The judgment circuit is used for judging whether the current bus line is grounded at the neutral point via a small resistor according to the electrical characteristics of the current bus line. The zero sequence differential protection circuit is used for starting zero sequence differential protection and outputting a control signal to turn off the switch of the current bus line if the current bus line is grounded at the neutral point via a small resistor. The invention further discloses a distribution network bus protection method with a grounding mode automatic identification function. With the distribution network bus protection device with a grounding mode automatic identification function provided by the invention, the problem that the bus of a distribution network cannot be protected under change of the grounding mode is solved.