The present invention discloses a sensor assembly for a passenger conveying device, a safety system and the passenger conveying device, wherein the sensor assembly (300) comprises an optical fiber (16) disposed along a length of a skirt board of the passenger conveying device; a light source (21) disposed at a first end of the optical fiber (16), light of the light source being incident into the optical fiber; and an optical receiver (22) disposed at the first end of the optical fiber (16), the optical receiver (22) receiving backwards scattered light from the optical fiber and being capable of sensing a signal indication of the backwards scattered light, wherein the optical fiber (16) is associated with a sensing element such that the sensing element causes deformation of the optical fiber when the sensing element is subjected to a pressure (P), and the optical receiver (22) is capable of sensing a change in the signal indication of the backward scattered light caused by the deformation of the optical fiber (16). The present invention can sense a situation in which foreign matters are clamped between the skirt board and a foot board of the passenger conveying device at the earliest time and take countermeasures in time.