Abstract: Based on the theory of string (rope) vibration, with the overhead skidding single span cableway with full suspension reinforcement as an example，the carrying rope bouncing and the free vibration due to the instant elastic energy release at cargo's unhooking are analyzed.The unhooking vibration model is established and the natural angular frequency, the period, the wavelength, the main vibration mode，the free modal vibration， and the total energy are discussed，and illustrated by 3D graphics.The results provide some guidance for the installation design, the improvement of the technology and the safety code of practice for forestry aerial ropeways.