The invention discloses a weighing device for a packaging machine. The weighing device for the packaging machine comprises a main body tank and a bearing plate, wherein a hydraulic oil pump is weldedonto one side end surface of the upper part of the main body tank; a hydraulic cylinder is arranged on the upper end surface of the hydraulic oil pump; a hydraulic rod is arranged on the hydraulic cylinder; a push plate is arranged at the tail end of the hydraulic rod; a light-emitting diode (LED) screen is fixedly arranged on the upper surface of the hydraulic cylinder through a support; buffer springs are fixedly arranged at the lower end of the bearing plate; weighing sensors are arranged at the lower ends of the buffer springs; a rotary rod is rotatably arranged on the main body tank; a discharging plate is fixedly arranged on the rotary rod; a holding tank is arranged in the main body tank; a battery ja is arranged in an inner wall of the main body tank and is connected onto the innerwall of the main body tank through an electric wire; fixed rods are welded to two sides of the side end surface, close to the hydraulic oil pump, of the main body tank; and the two fixed rods are connected through a push-pull rod. According to the weighing device for the packaging machine provided by the invention, a weighing error is reduced, and the integrity of an object fallen onto the devicecan be further ensured.