A binocular stereo vision maize leaf motion monitoring system was proposed, the system includes a binocular camera, horizontal movement module, the vertical movement module, the image acquisition card, and a computer. The supporting structure holds camera above the measured maize leaf, and the camera is able to capture image pair at 30f/s. An image processing program includes image acquisition, image pre processing, markers extraction, sub pixel edge refinement, 3D reconstruction and other modules. A fluorescent ball(diameter 0.35cm )with high reflectivity was chosen as a marker, and its intensity is higher than the background environment which makes it easier to extract contour of ball out of background. The spherical marker will keep its circular shape more or less after perspective projection. In order to further improve the accuracy of stereo matching, a sub pixel edge detection method based on gradient magnitude was adopted. In the simulation experiment, the camera was set away from the measured object about 50cm, the system measurement deviation was 0.0139cm, which is able to detect the small changes of leaf position. In field experiments, the actual measurement of the movement leaf caused by growth and physiological responses achieved the desired results.