Abstract: Abstract: The inclined inserted grafting machine is mainly used for melon and vegetable grafting，and the grafting operations include rootstock clamping, rootstock punching, scion clamping, scion cutting, and scion inserting to the rootstock. The seedling pressing mechanism has been commonly used to flat rootstock cotyledons and expose the growing point to make sure the normal operation of rootstock punching and scion inserting inclined during the grafting operation of vegetable grafting machine. Due to the structure of the seedling pressing mechanism being complex and flatting operation being time-consuming, an air suction clamp of rootstock cotyledons has been developed to simplify the structure of the rootstock clamping mechanism, and the productivity of grafting could be improved. The cotyledons are being pressed into the suction holes of the air suction clamp while the rootstock was placed into the air suction clamp, and then are adsorbed to the upper surface of the air suction clamp through negative pressure. Using standard seedlings of fig-leaf gourd rootstock seedlings and cucumber scion seedlings which were normally used in grafting production as experimental material, determination tests on rootstock cotyledons flatting property and optimization tests of structure and the operation parameters on air suction clamp of rootstock cotyledons were conducted to determine the optimized structure and operation parameters of the air suction clamp, and a performance comparison test between the rootstock clamp with seedling pressing mechanism and air suction clamp of rootstock cotyledons based on 2JC-600B inclined inserted into the vegetable grafting machine was conducted. To discuss the effects on the success rate of rootstock cotyledons flatting and success rate of grafting by rootstock types, skilled degree of the grafting operator, and time of placing rootstock. Results indicated that, with 0.25 MPa of working pressure of the pneumatic system, 4 mm of diameter of suction hole, and 30 mm of distance from suction hole to growing point, flatting effect of air suction clamp of rootstock cotyledons was optimal, with 100% success rate of cotyledons flatting. Comparing to rootstock clamp with seedling pressing mechanism，using the air suction clamp of rootstock cotyledons could lighten the effects of the operator level on the operating performance of the grafting machine and improve the success rate of rootstock cotyledons flatting and grafting significantly. For skilled operator, using the air suction clamp for grafting could reduce the time of placing rootstock under the grafting requirement, and the productivity of grafting could be increased from 514 plants/h to 600 plants/h, by 16.7%. With 3.5s of time of placing rootstock, the combination of air suction clamp and skilled operators, success rate of rootstock cotyledons flatting was at 95%, the success rate of grafting was 94%, the productivity of grafting was at 600 plants/h. These results could fulfill the production requirements of grafting and be used for a reference to design an inclined inserted grafting machine.