Abstract: For transplanting vegetables plug seedlings, it is difficult to directly pick up seedlings from the tray cells. Damages of root lumps of plug seedling happen all the time in extracting. In this paper, a root lump loosening mechanism using air jets to eject vegetable plug seedlings making for transplanting was designed and evaluated. It consisted of air jets, a linear module, a double-rod cylinder, a control system and some other supporting parts. The step transmission of the air jet along the horizontal direction was performed using the linear module, which was a synchronous belt system. The air jet′ motion along the vertical direction up and down for ejecting plug seedlings was moved by the double-rod cylinder. For high blowing rates, wholes rows of air jets aiming for each drain hole was designed. In this arrangement, the seedlings could be loosened row by row. With a row of air jets blowing the seedling plugs from the drain holes of the tray cells, air pressures along with the force of the plungers effectively loosened seedlings. It would be good for manual pulling seedlings or automatically picking up seedlings from the tray cells. Based on the integrated design and analysis, the air pressure range of succeeding in loosening seedling plugs was 0.098-0.235 MPa using the air jet at the diameter of 5 mm. Under this condition, the seedlings appeared to be most effective in the loosening and not in destroy of the root soil. Meanwhile, the air jet could eject each drain hole at the bottom of the 128-cell tray. Being the first prototype, its optimal machine parameters were examined under various conditions. In the optimum tests, it was found that the air pressure of the air jet plungers exerted the greatest effect on the integrated ratio in loosening seedling plugs, and followed by the moisture content. Other factors such as the seedling age, the air flow rate and the air jet with sponges or not had no significant effects on the integrated ratio in loosening seedling plugs. In reality, it would probably be a moderate air blast for blowing of the plug seedlings from the tray. If the moisture content of root lumps of the plug seedlings was less than 55%, the cohesion forces between the roots and the tray cell walls would increase. In this case, wetting the roots might serve to reduce the adhesion making for blowing. For cucumbers seedlings, when the air pressure of the air jet plungers was 0.2 MPa, the root zone moisture was 55%-60%, the seedling age was 25 d, the airflow circuit was fully open at the outlet of 4 mm, and the air jet had no sponges, the best intact rate succeeding in loosening root lumps of plug seedlings was achieved. Finally, the overall loosening performance test was carried out. The intact rate of seedling and root lump in loosening root lumps by blowing was more than 96%. It needed about 48 s for finishing loosening the whole tray of plug seedling. The loosening mechanism using air jets to eject vegetable plug seedlings has a good performance, which can meet the actual requirements.