To understand the mooring energy during positioning,the expressions of four items concerning mooting line energy are presented based on a finite element model,including gravitational and elastic potential energy,kinetic energy and dissipated energy due to mooting-induced damping.In a static case,the force calculated from the derivative of potential energy with respect to distance is compared with that of direct calculation.The results are found fit well,which indicates the law of conservation of energy and also shows the correctness of the potential energy results.For the cases of a single mooring line with the attachment point oscillating with different amplitudes in horizontal or vertical direction(corresponding to surge and roll motions respectively),and the case of the mooring line with a horizontal bichromatic oscillation on the attachment point,the time history of the first three items are calculated and analyzed,also,the indicator diagram for mooting-induced damping are given.These results reveal the energy state of the mooring line and can provide a better understanding of how the mooting line works.