The invention discloses a belt conveying device of a circular knife machine. The belt conveying device of the circular knife machine comprises a vertical installing plate, a circular knife machine body, a motor, a tightening wheel, first conveying wheels, second conveying wheels and a fixing rod. The circular knife machine body is fixedly connected with the rear face of the vertical installing plate. The motor, the tightening wheel, the first conveying wheels and the second conveying wheels are fixedly connected with the front face of the vertical installing plate. The fixing rod is fixedly connected with the front face of the side, close to the fixing rod, of the vertical installing plate. A collecting box is fixedly connected with the surface of the fixing rod. The surface of the collecting box is movably connected with a moving box, and a pulling handle is fixedly connected with the middle of the front face of the moving box. The front face of the collecting box is further fixedly connected with a fixing device, and the fixing device is movably connected with the moving box. According to the belt conveying device of the circular knife machine, the effects that a mold cutting piece processing material can be collected by the moving box taken down conveniently, the moving box can be conveniently taken down when a certain amount of materials are collected, and therefore collected materials can be taken out conveniently are realized.