With the development of single seed sowing and precision seeding technology in China,higher requirements are put forward for the quality of single seed. In response to the current demand for fine seed selection in agricultural production,an online single seed detection and sorting device was designed. The device consisted of a feeding device, a detection unit, a sorting unit and a control system. The feeding device was composed of two sets of linear vibration devices, which can realize the flattening of the grains through two-stage vibration, and cooperate with the conveyor belt to complete the single granulation of the grains. The detection unit obtained the seed image in real time by the high-speed industrial camera, and transmitted it to the upper computer for detection and analysis. The sorting unit was made of sorting components and air compressor, which was used to remove the identified damaged or moldy grains. The control system controlled the sorting unit to complete the sorting according to the detection result and the position of the seed in the image. Furthermore, images of 3600 corn seeds (1200 normal seeds,1200 moldy seeds, and 1200 damaged seeds) were collected by using the built device, and image processing algorithms were used to obtain the 18 color and 12 morphological characteristics of a single seed, and the partial least squares discrimination analysis method (PLSDA) was used for discriminant analysis, and the detection models of moldy and damaged seeds were constructed respectively. Then the online verification experiment was carried out by using the built device and model. The results showed that the sorting rate of the device was greater than 300 seeds/min; the sorting accuracy of the mildew model was higher than 95%, and the sorting accuracy of the damaged model was higher than 89%. The device can realize the full automation of corn seeds from feeding to sorting, and can detect and sort moldy and damaged corn seeds in real time.