Abstract: A numerical model was established using finite element method in time domain for fiber mooring lines. For different water depths, the displacementlateral force relations were compared for three types of mooring system and the corresponding effective utilization rates were calculated. This shows that it is more competitive for the taut mooring system using lightweight fiber lines than the other ones in deep water. The dynamic analysis of the polyester mooring line was conducted, where a linear material property was proposed to fit the nonlinear stressstrain relations, the result was compared with the nonlinear elastic model. It was found that the simulation by linear fitting to the material properties in the numerical model can not obtain a reasonable result and it is necessary to use nonlinear elastic model for fiber lines. For the mooring system of a Spar, three types of fiber lines were used respectively. Dynamic analysis was performed and all tensions of the threetype lines were compared. The results show that polyester mooring lines present the best performance.