A large size element measuring device based on the machine vision comprises a chassis, a large calibration block and a small calibration block, wherein the length ratio of the large calibration block and the small calibration block is 3:2-2:1, an L-shaped mobile station is connected on the chassis in a sliding way, a support bar is connected on the vertical arm of the L-shaped mobile station in a sliding way, and the sliding direction of the L-shaped mobile station is perpendicular to the sliding direction of the support bar, a rotary block is rotatably connected on the support bar, and the rotational motion plane of the rotary block is perpendicular to a plane which is decided by the sliding direction of the L-shaped mobile station and the sliding direction of the support bar, a camera support plate is rotatably connected on the rotary block, and the rotational motion plane of the camera support plate is perpendicular to a plane which is decided by the sliding direction of the L-shaped mobile station and the sliding direction of the support bar, a camera is arranged on the camera support plate, a translation device is arranged on the chassis, a white background plate is arranged on the translation device, and is located under the camera, and a steel rule for observing the movement distance of a tray is arranged on the chassis.