In order to achieve the on-line nondestructive assessment for vegetable seedling growth, the method and device for measuring the seedling’s leaf spatial morphology based on photometric stereo vision was introduced, and the morphology information, including seedling leaf’s inclination angle, length and size. The 15~30d pepper seedlings were adopted as research objects, and the test device for measuring their canopy leaves was built, which involved the four different LED lights’ orientation calibration and the image color’s linear correction referring to the D65 palette’s color variation under the various illumination. According to the light reflexive relation on the calibration ball from the LED lights to the camera, the spatial orientations of illuminants under the camera coordinate were determined. And the image color correction was supposed to overcome the color distortion caused from the lights’ luminance fluctuation. According to the seedling leaves’ light-shadow feature under various illuminants, the discrete gradient information along the leaf’s main vein was obtained based on photometric stereo vision. And referring to the gradients vectors, the leaf’s space plane was fit by adopting the least-square principle. The leaf’s inclination angle was measured as the angle between the fitting plane and camera imaging plane, thus the actual spatial leaf size also could be accurately measured on the basis of the image size. As the test result shown, compared with the manual measurement result, the auto-measurement method had an average errors of 6.29° for leaf inclination angle, 3.82mm for leaf length, and 56.53mm2 for leaf size, and the determination coefficients on the length and leaf size measurement were 0.9363 and 0.8664, respectively. Besides, the measuring result would be more accurate for the younger seedling with fully-opened and unoverlapped leaves. 