Aiming at the problems of low counting accuracy due to seed accumulation, sticking and shading phenomena in the wheat seed testing process, a high-throughput wheat seed vibration separation device was designed based on the principle of electromagnetic vibration. The main influencing factors of the degree of seed dispersion and separation were discussed by analyzing the forces, and the secondorder dispersion coefficient was introduced to establish the seed dispersion grade evaluation method. On this basis, the YOLO v7-ST model was then built by using the Swin Transformer module and was tested for counting performance under different discrete degree levels. The experimental results showed that the mean counting accuracy, F1 value and mean counting time of the YOLO v7-ST model were 99.16%, 93% and 1.19s under the three dispersion levels, respectively. Compared with that of the YOLO v7, YOLO v5 and Faster R-CNN models, the mean counting accuracy was improved by 1.03 percentage points, 2.34 percentage points and 15.44 percentage points, respectively, and the F1 values of the comprehensive evaluation index of the model was increased by 2 percentage points, 3 percentage points and 16 percentage points, respectively. The mean counting time was decreased by 0.41s and 0.36s compared with that of YOLO v5 and Faster R-CNN, respectively, and it was only 0.09s slower than that of the YOLO v7 model. Overall, the YOLO v7-ST model provided accurate and efficient detection of grains under various discrete degree levels, significantly improved the efficiency of wheat breeding.