The invention discloses an automatic three-layer protection system of a distribution network. The automatic three-layer protection system of the distribution network comprises a distribution master station, a distribution substation, distribution remote terminals and a communication channel. The distribution master station, the distribution substation and the distribution remote terminals are respectively connected onto the communication channel; the distribution master station is provided with a distribution network control host; distribution network control extensions are arranged in the distribution substation; the distribution network control host and the distribution network control extensions are connected onto the communication channel; the distribution substation is arranged in a transformer substation; each distribution remote terminal comprises distribution terminal equipment and ring main unit terminal equipment; each piece of distribution terminal equipment and each piece of ring main unit terminal equipment are respectively and electrically connected with a corresponding distribution switch; the distribution switches are arranged on a distribution line dropped output to user equipment from transformers of the transformer substation. According to the automatic three-layer protection system of the distribution network disclosed by the invention, the three-layer protection of the distribution network system is realized by the distribution master station, the distribution substation and the distribution remote terminals. The automatic three-layer protection system of the distribution network is high in reliability and high in fault point judgment and isolation speed. The relevance and distribution switch requirement on distribution network system topology is lowered.