For the purpose of decreasing the investment of labour force in the process of vegetable grafting, a vegetable grafting robot operated by one person for Cucurbitaceous seedlings cultivated in plug trays was designed. The machine utilized the root-cutting grafting method. During working, the operator delivered respectively the stock and scion seedlings from plug trays on the left-hand and right-hand sides to seedling-providing platforms. The seedlings triggered the touching switches and then the machine completed automatically the subsequent motions of gripping, cutting, jointing, fixation and discharge controlled by PLC program. A theoretical analysis of promotion of grafting efficiency was done. In theory, the operating efficiency for one person of this robot can be promoted by 100%, compared with the old type of 2JSZ—600II grafting robot. And the analysis suggested that with the operating qualification promoting, the efficiency would be higher. Experiment results showed that the grafting success rate of the machine could reach up 95% and its grafting speed was approximately 455 seedlings per hour. Compared with previous grafting robots whose grafting efficiency was merely 600 seedlings per hour operated by two people, the machine’s working efficiency of per capita was improved by more than 50%. Therefore, the upgraded machine operated by one person was quite capable of developing the grafting labour efficiency.