The invention provides a mechanical protection device for a die assembly of a plastic injection and blowing molding machine, comprising a cross beam and a worktable, wherein the cross beam is connected with the worktable through a stand column; the worktable is provided with a lower die of a mounting mould and the cross beam is internally provided with an opening/closing die air cylinder; the opening/closing die air cylinder is connected with a movable template and an upper die of the mould is connected below the movable template; the upper die of the mould corresponds to the lower die of the mould; the mechanical protection device provided by the invention is characterized in that: the cross beam is fixedly provided with a fixed plate and the fixed plate is transversely provided with a plug air cylinder; a piston rod of the plug air cylinder is connected with a plug and a hook is vertically arranged on the movable template; and the pin is matched with the hook. The mechanical protection device provided by the invention is matched with a hydraulic protection device of a machine so that the machine has double die assembly protection functions, and the personal safety of workers and the mould safety are ensured.