Abstract: The potted-seedling growth state varies in the tray. Transplanting is the key in the nursery seedling process. In order to improve the survival rate of a transplanted potted-seedling, and solve the emergence problems such as seedlings growth, or irregular or broken seedlings, the fitness information of the perpendicularity and height of transplanted potted seedlings was comprehensively evaluated, and filtered out potted seedlings meeting the transplanting requirements. The potted-seedling jacked up by the push rod of the image acquisition system can be rotated 90°. A camera captured two images of the potted-seedling before and after it was rotated 90°. The gray-value probabilities histogram of the grayscale images RGB channels existing concentrated areas. At first，the image was pre-processed by 24-bit RGB source image converting to 8 bit grayscale algorithm, median filtering algorithm and gray stretching algorithm. Then, the trunk features of the potted-seedling were extracted by the image processing algorithms of thinning, horizontal expansion, and vertical erosion. Finally, the key points of every potted-seedling trunk were extracted by a Harris corner detection algorithm of 3×3 Gauss templates of the standard deviation was 0.65, and the fitting line was obtained by the weighted least-squares linear fitting with the key points, and the converted line slope was used as the identification parameter of the potted-seedling upright, and found out the maximum y-coordinate difference of all corners coordinates in each strain of potted-seedling, 110% of the difference was used as the identification parameters of the potted-seedling height. The perpendicularity and height of potted-seedlings had to meet evaluation requirements before being considered suitable for transplant. The perpendicularity and height of 30 strains of a pepper potted-seedling in twelve images were distinguished by machine vision technology at the 0 and 90°position, and the average time consuming of each image being processed was 0.35 s. According to evaluating indicators of the perpendicularity (45°＜α＜135°) and height (H＞105 mm), it was determined that five potted-seedlings were suitable for transplanting, and wherein the measurement results of two potted-seedlings were converse using the vision measurement method or the manual measuring method. The error rate was 6.67% between the machine vision recognition results and the manual measurement results. The main reason for the deviation was that the manual measuring accuracy was affected by the leaves of the potted-seedlings obscuring the stems and the vibrations of the transplanting machine causing location changes during the process of rotating 90°.