As a catenary riser, unbonded flexible pipe (UFP) has the advantages of convenient installation, recyclability, flexibility, anti-corrosion and large design space. To analyze the residual fatigue life of in-service unbonded flexible riser (UFR), a global model of riser is established in this paper. By analyzing the distribution of configuration, tension, bending moment and bending curvature along the riser under static and dynamic loads, the most dangerous position and dynamic response are determined. And then, the residual fatigue life of the UFR is calculated. The calculation results show that the fatigue life of the UFR is greatly affected by the pipe annulus condition, and the dry annulus condition is 4.6 times that of the wet annulus condition. It is concluded that when evaluating the remaining fatigue life of an inservice UFR, the S-N curve of the tensile amour layers must be calculated according to different annular conditions, so that the fatigue life can be accurately obtained. Summarily, this paper provides an effective method for calculating the residual fatigue life of in-service UFRs.