The invention discloses a single-rolling-brush type seedling trimming mechanism disposed on an automatic cucurbit grafting machine and belongs to gardening vegetable seedling raising production equipment. A horizontal movement driving assembly and a horizontal slideway frame assembly are assembled in parallel on a frame assembly, an assembled plate assembly provided with a height adjusting and push-pull driving plate and a vertical movement seat plate is movably assembled on the horizontal slideway frame assembly, the horizontal movement driving assembly is connected with the height adjusting and push-pull driving plate, a vertical movement driving assembly is assembled on the assembled plate assembly and positioned between two limiting slideway plates, the upper side of a connecting plate is connected with a driving part of the vertical movement driving assembly, a motor with a shaft type brush roller is mounted on the lower side of the connecting plate, a supporting plate is disposed on the outer side of the frame assembly, and the shaft type brush roller is in inserted or extracted match with a vertical strip slideway through hole on the supporting plate. The single-rolling-brush type seedling trimming mechanism is novel and reasonable in structure, simple and convenient to operate, high in operating quality and efficiency and reliable to use.