The auxiliary tool comprises a rectangular bottom frame (1) and battens (2) which can be tightly arranged and installed on the upper surface of the bottom frame in sequence and have the same width, the two ends of each batten are installed on the bottom frame through screws or bolts (3), and the width of each batten is the same as the width of a single hole unit of the floating seedling growing tray. The device is simple in structure, convenient to use and flexible to adjust, and is particularly suitable for random interlaced substrate loading used in experiments of sowing multiple varieties of seedlings in the same floating seedling raising tray.