Based on the AQUA module of Abaqus, the dynamic characteristics of synthetic fiber mooring line under external excitation are analyzed. The dynamic stiffness characteristics of the mooring line are simulated by the UMAT subroutine in Abaqus. Taken the taut-wire mooring system of a Spar platform at the depth of 1 500 m as an example, the static stiffness and dynamic stiffness of the mooring system are calculated, and the changes of tension in two cases are compared. It is recognized that the tension and stiffness of the whole line are the same by the traditional method, taken the head end and tail end of the line as the research object, the difference between the dynamic tension and dynamic stiffness are compared, and it is found that there is error when using the traditional method. The influence of self weight and current force on the tension and dynamic stiffness of the mooring line is analyzed, and it is found that the self weight and current force can not be ignored in tension calculation. The influence of external excitation amplitude and period on the tension and dynamic stiffness of the mooring line is analyzed, and the results show that the peak tension increases with the increase of external excitation amplitude and the periods of the tension and dynamic stiffness change with that of external excitation period.