The present invention discloses a distance detecting sensor, comprising: a casing, focusing lenses, a circuit board mounted with several electronic elements, and an emitting device emitting infrared light and a receiving device receiving and sensing a reflected infrared light. Wherein, the casing comprises a main body and two round openings on the top surface of the main body. The lenses comprise an emitting lens and a receiving lens arranged at the openings of the casing. The circuit board is mounted in the main body of the casing; the emitting device is an infrared emitting diode (LED), emitting infrared light toward the emitting lens. The receiving device is a distance detecting sensor module, which senses the reflected light focused by the receiving lens. The distance detecting sensor further comprises an emitting light guide unit arranged between the emitting lens and the emitting device, and the emitting light guide unit comprises small round holes at the emitting tube core of the emitting device. The present invention has higher detection accuracy and improves the overall detection performance of the sensor.