Abstract: Abstract: In order to reduce the breakage rate of the broccoli seedling during mechanized planting and to avoid the transplanting failure caused by the discordance between planting nozzle and seedling while the planting nozzle has arrived at the planting location but the seedling has not slipped to the bottom of planting nozzle, the orthogonal experiments based on agronomic requirements has been carried out in this paper. The volume of soil block (represent plate size), seedling age, and moisture content of soil blocks are selected as the experimental factors. Every factor has three levels. One experiment has been carried out to test the compressive strength of soil blocks under different schemes. Through using the universal material testing machine, the relationships between compressive force and compressive amount have been obtained and expressed as curves. In order to analyze these curves, the compression elasticity of the soil block has been proposed, which was defined as the straight slope between point D (starting point of linear elastic) and point E (yield point). Then, several sets of compression elasticity and yield limit under different schemes have been obtained. Analysis results show that the compression elasticity increases at first, then decreases with the reduction of the volume of soil blocks, while the yield limit decreases with the reduction of the volume of soil blocks. Both of them have no significant relationship with seedling age, but decrease with the increase in moisture content. Another experiment was carried out to test the motion resistance coefficient between seedling and planting nozzle. The broccoli seedling was put on an incline, then the process of broccoli seedling sliding along the incline was recorded by the high-speed camera. The sliding acceleration along the incline of broccoli seedling was obtained by video processing technology. Afterwards, the motion resistance coefficient was derived by using Newtonian mechanics theory. Analysis results show that the motion resistance coefficient decreases with the reduction of soil block volume, and increases with the increase of both the seedling age and moisture content. The mechanics model of the colliding process between seedling and planting nozzle has been built, and the highest relative speed allowed was obtained from the model. In order to avoid the breakage of seedling, meanwhile the motion resistance coefficient shouldn't be too high, a comprehensive scoring method was applied to evaluate the combinations of soil block volume, seedling age, and moisture content. Four combinations were chosen by comparing the scores. In order to achieve the best combination, the field planting simulation experiment was conducted. This experiment was done indoors by using a rotating circular soil tank driven by the friction of tires. Breakage rate and rewind rate were obtained from this experiment. The best combination that is suitable for mechanized planting of broccoli seedling was obtained: medium soil block (128 holes plate), 2-3 leaves, and water content at 63%. This study provides reference for the design of planting mechanism.