An automatic plastic discharging apparatus of a fully automated flatbed shoulder injection machine, comprising a work platform (1), a mobile material mesa mechanism (2), a material discharging mechanism (3), and a material storing mechanism (4). The mobile material mesa mechanism (2) comprises a material mesa frame (5), a mobile material base (6), and a power motor (7). The material discharging mechanism (3) comprises a material discharging motor (9), a pressure rod (10), a plastic injecting hydraulic cylinder (11), and a thermally-insulating flow channel (12). The material storing mechanism (4) consists of a material hopper (14), a material storage motor (15), and a material storage wheel (16). The automatic plastic discharging apparatus of the fully automated flatbed shoulder injection machine employs the automatic plastic discharging apparatus, forms multiple work positions in one step, increases production efficiency, and saves labor costs; the equipment employs a servo motor in place of hydraulic driving equipment, reduces work noise, and solves the problem of pollution brought forth by oil leak of hydraulic equipment.