The utility model discloses a communication expansion device of an arc light detecting relay. The communication expansion device of the arc light detecting relay includes a first one-way communication interface provided with an input terminal connected with a current collector through communication medium; an instruction generating circuit connected with an output terminal of the first one-way communication interface; a multi-channel communication interface connected with a first microprocessor and at least one arc light detecting relay; an information collecting circuit connected with the multi-channel communication interface; and a second one-way communication interface provided with an input terminal connected with a second microprocessor and provided with an output terminal connected with a monitoring system through the communication medium. According to the utility model, no transformation is needed for a switch cabinet and current information of a power source point can be transmitted to the arc light detecting relay. Besides, statuses and action information of the arc light detecting relay can be uploaded.