A ball-rolling type orientation sensor includes a housing, a light emitter, two light receivers, and a rolling ball. The housing has a ring-shaped tunnel and a first opening connecting to the tunnel and two second openings respectively located on two sides of the first opening. The light emitter is arranged at the first opening and emitting light into the tunnel through the first opening. The light receivers are respectively arranged at the second openings and receiving light from the tunnel through the second openings. The rolling ball is arranged in the tunnel, whereby while the ball-rolling type orientation sensor is tilting, the rolling ball rolls toward the direction of gravity force, a portion of light emitted from the light emitter is reflected to one of the light receivers by the rolling ball, the light receivers respectively receive light with predetermined intensities and correspondingly output electric signals with predetermined strengths.