The invention discloses an online weighing system being suitable for an OVD process, which includes an upper gripper mechanism, a lower support mechanism, and a weighing unit. The upper gripper mechanism includes a pedestal, a linear slide rail, and an upper rod-holding gripper which is connected to upper end of a powder rod and is connected to the lower end of a rotary shaft; the upper end of the rotary shaft is connected to the weighing unit through a horizontal bearing and a horizontal bearing base; a rotary outer sleeve tube is arranged outside the rotary shaft and is connected to the pedestal through the linear slide rail; the pedestal is connected to a chamber wall of a deposition chamber; the lower support mechanism includes a lower gripper pedestal which is connected to a bottom board of the deposition chamber, and a lower gripper elastic member arranged around the lower end of the powder rod; and the lower gripper elastic member is connected to the lower gripper pedestal through a connection mechanism. The system is free of interference between weighing function and self-rotational movement, so that high rotation precision of the powder rod is maintained and the weight of the rotating powder rod can be accurately measured in real time.