In order to understand the production effects and influencing factors of the 2JC-500 automatic grafting machine, a production test for watermelon had been done and the effects of watermelon seedling shapes on working performances were studied. The results indicate that, three situations ( such as cotyledon flare angle of stock lower than 45°, curving hypocotyl of watermelon scion, and cotyledon asymmetric with hypocotyl ) have significant effects on the quality of perforating stock and jointing stock with scion, respectively. When cotyledon flare angle of stock is larger than 45°, hypocotyl of watermelon scion is unbent and symmetric with hypocotyl, grafting success rate of 2JC-500 automatic grafting machine can be above 90%, and the productivity can be 450 seedlings per hour.