A full-automatic method for manufacturing plant-fiber molding products, wherein the method comprises the following steps: Step 1: pulps are continuously made into wet semi-finished product by means of a suck-filter forming device, the wet semi-finished product is alternatively fed into hot-press molds of a left hot press mold solidifying device and a right hot press mold solidifying device after being heated to a certain temperature for hot-press drying and solidifying, wherein dried and solidified products are fed into a left positioning collection tray (A5.1) of a left positioning collection device and a right positioning collection tray (A6.1) of a right positioning collection device respectively from a left hot-press top mold and a right hot-press top mold, and are positioned therein to be transferred to be margin trimmed; Step 2: the left positioning collection device delivers the dried and solidified products to be margin trimmed to a left transition station and the right positioning collection device delivers the dried and solidified products to be margin trimmed to a right transition station; the products to be margin trimmed are transferred to a position to be margin trimmed of a margin trimming device by a transfer device positioned on the left transition station and the right transition station, and then the margin trimming device withdraws the products to be margin trimmed from the position to be margin trimmed, delivers the products to the margin trimming position for margin trimming, and then delivers margin trimmed products to a destination position and expels or removes margin trimmed scrap from the margin trimming position; and Step 3: repeating Steps 1 and 2; characterized in that only one single margin trimming device is fed by both of the left and the right transition stations receiving the dried and solidified products to be margin trimmed wherein said dried and solidified products are produced by the hot-press molds. Step 1: pulps are continuously made into wet semi-finished product by means of a suck-filter forming device, the wet semi-finished product is alternatively fed into hot-press molds of a left hot press mold solidifying device and a right hot press mold solidifying device after being heated to a certain temperature for hot-press drying and solidifying, wherein dried and solidified products are fed into a left positioning collection tray (A5.1) of a left positioning collection device and a right positioning collection tray (A6.1) of a right positioning collection device respectively from a left hot-press top mold and a right hot-press top mold, and are positioned therein to be transferred to be margin trimmed; Step 2: the left positioning collection device delivers the dried and solidified products to be margin trimmed to a left transition station and the right positioning collection device delivers the dried and solidified products to be margin trimmed to a right transition station; the products to be margin trimmed are transferred to a position to be margin trimmed of a margin trimming device by a transfer device positioned on the left transition station and the right transition station, and then the margin trimming device withdraws the products to be margin trimmed from the position to be margin trimmed, delivers the products to the margin trimming position for margin trimming, and then delivers margin trimmed products to a destination position and expels or removes margin trimmed scrap from the margin trimming position; and Step 3: repeating Steps 1 and 2; characterized in that only one single margin trimming device is fed by both of the left and the right transition stations receiving the dried and solidified products to be margin trimmed wherein said dried and solidified products are produced by the hot-press molds.