A laser vision based measurement system consisting of a camera and a laser sheet that scanned the plant vertically was developed to measure the stem diameters and leaf lengths automatically. The 3D point cloud was obtained with the laser sheet scanning the plant vertically, while the camera videoed the process of laser scanning. Laser line centers were extracted by improved centroid method. The 3D point cloud structure of the sample plant was obtained. For leaf length measurement, iteration method for point clouds was used to extract the axis of the leaf point cloud set. The centroid of the subset of points was calculated and taken as the next axis point. Leaf length was calculated by curve fitting on these axis points. In order to increase the accuracy of curve fitting, bi-directional starting point selection was used. To evaluate the method in a sample of 8 water spinaches, the lengths of leaves and diameters of stems were measured manually and plotted versus their automatically measured counterparts. The accuracy of leaf lengths and stem diameters are 95.39% and 94.55% respectively. The tests proved that laser vision based method could be used on plant geometries measurement in greenhouses costly and portably.