The graft robot (named ZSTU-GR01), developed by authors, is an automatic machine for grafting fruits and vegetables with parallel insert method. The objective of this research is to test the performance of ZSTU-GR01 automatic graft robot and find out the most suitable seedling parameters for grafting. Thus a PLC program and a grafting experiment for graft robot were developed. The experimental results showed that the total grafting speed was 514 seedlings per hour, and total success rate was 84%. Eight independent comparison experiments showed that the most suitable seedling parameters for grafting were: rootstock diameter 3.5-4.5(mm); scion diameter 2-3(mm); rootstock stem and scion stem straight; angle of rootstock cotyledons close to 180 degrees.