Abstract: Grafting seedling technology of vegetable is very extensive application in worldwide. Currently, the aging of employees and the shortage of employment have posed a great challenge on the seedling production, due to the seedling enterprises previously relied fully on grafting technical workers. Alternatively, a grafting machine can be used to improve the efficiency and quality of grafting seedlings, as well as the standardized and automatic operation. However, an artificial feeding seedling is still in manual in most grafting machines, and thereby to greatly limit the production efficiency, particularly on the popularization and application of grafting seedling technology. Adsorption block generally serves as a feeding and positioning device of a rootstock in a new grafting machine. The simulation test can be used to design the working face profile and structural parameters of adsorption block, further to improve the flexibility and safety of rootstock. It can also greatly shorten the design cycle of adsorption block. In this study, a seedling positioning device of rootstock was designed, based on the principles of air pressing seedling at a positive pressure and adsorption positioning at a negative pressure, in order to rootstock cotyledon damage and petiole splitting during the artificial feeding seedling of grafting machine. The external geometric parameters of cucurbita moschata seedlings and the breakpoint pressure of cotyledon were measured for the structural and working parameters of adsorption block. A point fitting method was used to extract the trajectory equation of cotyledon back development curve, which was used for the profile design of working face in an adsorption block. A finite element model of device was established under the given boundary conditions. A CFD software was selected to dynamically simulate the airflow field inside the adsorption block, thereby to obtain the distribution of flow field in the gas chamber, with emphasis on the influence of various factors on the adsorption force of rootstock cotyledon. A simulation orthogonal test was used to determine the optimal structural parameters of adsorbent block. The influence of various factors on the average suction was ranked in order, the outlet negative pressure, diameter, depth. When the negative pressure at the outlet of adsorption block was 3kPa, the pore diameter was 1 mm, and the depth of suction hole was 4 mm, the pressure of 21 suction holes was less than the rupture point pressure of cucurbita moschata cotyledon, indicating that the adsorption block showed a good adsorption and localization ability for cotyledon. In the feeding seedling test, the adsorption success rate of cucurbita moschata cotyledon was 96.67%, the success rate of pressing seedling was 99.33%, the comprehensive feeding success rate of seedling was 96.03%, and the seedling injury rate was only 0.67%. The performance of device can fully meet the requirements of automatic feeding seedling for a grafting machine. The failure of cotyledon adsorption can be attributed to the inaccurate control of cotyledon direction and feeding seedling height, as well as the petiole splitting caused by relatively small cotyledon angle. The findings can provide a sound theoretical basis and design reference for automatic feeding seedling of grafting machine.