The bacterial fruit blotch (BFB) caused by Acidovorax avenae ssp. citrulli (Aac) is a sort of devastating seed-borne quarantine disease of cucurbits. The impact of seed infection was investigated to the disease severity of cucurbit rootstock seedling and the infection process of Aac during seedling stage through artificially inculcating cucurbit seeds with Aac.In greenhouse condition, the relationship between different carrier amount of bacteria and the disease level of BFB was established. The results indicate that during the seed-borne infection process, the Aac infected the cotyledons firstly, then infected the hypocotyls and colonized in the xylem and phloem, caused the disease of the hypocotyls. Moreover, the higher amount of bacteria the seeds carried, and the higher disease rate and index the young seedling was. 