The invention discloses a metering device for a mechanical light sensation combined redundant water quality monitor. The metering device comprises a motor, a lead screw, a piston rod, a piston cavity,an infrared range sensor, a photoelectric range sensor and a controller. The motor is connected with the lead screw through a coupler. The lead screw is connected with the piston rod through a lead screw pair. The piston rod moves leftwards and rightwards in a piston cavity. A water inlet pipe and a water outlet pipe are connected with the piston cavity. Two ends of the infrared range detector are mounted on opposite sides of the motor and the piston rod. The photoelectric range sensor is mounted above a water storage device and faces the interior of the water storage device. The controller is connected with the infrared range detector and the photoelectric range sensor electrically. The metering device has the advantages that the volume of sample water of water quality sampling can be controlled accurately, accuracy and automation in water quality sampling can be realized, and accordingly, accuracy of water quality detection results is improved.