As one of the main configurations of the riser, top tensioned riser(TTR) encounters harsh environment in its whole service life. In order to ensure that the riser will fulfil its intended functions, a fatigue assessment should be carried out for each representative riser, which is subjected to dynamic fatigue loading. The fatigue life of TTR under the combination excitation of random waves, current and vessel motion is analyzed in this paper. The long-term stress histories of the riser are calculated and the mean stresses, the number of stress cycles and amplitudes are determined by rain flow counting method. The Palmgren-Miner rule for cumulative damage theory with a specified S–N curve is used to estimate the fatigue life of the riser. The corresponding numerical programs which can be used to calculate the response and fatigue life of the riser are compiled. The significant influences of internal flow velocities and low frequency motion of the vessel are analyzed in detail.