The invention relates to a photoelectric type arc light protecting system which is characterized in that an arc light unit, a current unit, a main control unit and a power supply are included, the arc light unit is used for managing and controlling an arc light expanding function, the current unit is used for managing and controlling a current detecting function. A plurality of arc light sensors are arranged in a switch cabinet. The arc light sensors are connected with the input end of the arc light unit. A current transformer is connected with the input end of the current unit. The output end of the arc light unit and the output end of the current unit are connected with signal input ports of the main control unit. The main control unit is provided with signal output ends which send tripping signals to a breaker I and a breaker II on a main side and a changing side of a transformer at the same time. Protection action is quick, reliability is high, applicability is high, and the problem that the fault probability of a medium-low voltage bus system is high is solved.