The invention discloses an arc sensor self-checking method and an arc protection device for medium-voltage and low-voltage switching cabinets. The self-checking method is implemented according to thefollowing steps: an arc sensor is illuminated with self-checking light at specified intensity and frequency; if an induction light signal is obtained, the frequency of the induction light signal is extracted, and whether the frequency of the induction light signal and the frequency of the self-checking light are identical is judged; if the frequency of the induction light signal and the frequencyof the self-checking light are identical, it is judged that the arc sensor runs normally, otherwise, it is judged that the arc sensor is affected by an external interference light source; and if no induction light signal is obtained, it is judged that the arc sensor or the light source of self-checking light fails. The arc protection device includes a self-checking light emitting unit, an arc sensor, an actuator, a signal acquisition module, a signal conversion module and a main control unit. Whether the arc sensor or the light source of self-checking light fails, whether the arc sensor runs normally and whether the arc sensor is affected by an external interference light source are judged based on the induction light signal. Therefore, faults can be quickly found, and the reliability of arc protection is improved.