The invention relates to a paper box forming device, in particular to a paper box positioning die-filling mechanism. A spindle and an auxiliary shaft are arranged inside a worktable, a primary driving cam is mounted in the middle of the spindle, two bilaterally corresponding secondary driving cams are arranged on the left side and the right side of the primary driving cam respectively and correspond to each other, the primary driving cam controls a pressing plate through a connector, the secondary driving cams are connected with the auxiliary shaft through connectors, two bilaterally corresponding clamp plates are fixedly mounted on the auxiliary shaft, a spring sleeves the middle of the auxiliary shaft, one end of the auxiliary shaft is abutted to an auxiliary cam, gradually rising transition surfaces and a raised surface are arranged on the end face of the auxiliary cam, and the raised surface is positioned at a high point between the transition surfaces. In the process of pressing down a die, the travel track of the clamp plates is determined according to the cams, a paper box is clamped and positioned by the clamp plates, die-filling accuracy is improved, so that the die and the paper box are more fitted, the technical scheme of performing driving control by a cylinder in the prior art is changed, the die-filling process is finished by means of mechanical linkage, and 50 paper boxes can be filled in dies per minute.