The invention provides a work piece measuring device which includes a vibration feeding mechanism, a measuring mechanism, a group discharging mechanism, and a feeding material pushing mechanism. The measuring mechanism has a measuring part of which the inlet is coupled to the discharge hole of the vibration feeding mechanism. The group discharging mechanism includes a conveyor belt coupled to the outlet of the measuring part of the measuring mechanism, different material boxes arranged in turn in the conveying stroke of the conveyor belt and corresponding to different measurement results of the measuring part, and a discharging material pushing mechanism used for pushing work pieces on the conveyor belt to the corresponding material boxes. The feeding material pushing mechanism is used for pushing work pieces output from the discharge hole of the vibration feeding mechanism to the measuring part of the measuring mechanism and to the conveyor belt of the group discharging mechanism. A measuring method is provided accordingly. Through the device and the method, work pieces can be fed automatically, and can be sorted and discharged to the different material boxes corresponding to different detection results after detection.