In order to accurately evaluate the durability stay cables of parallel steel wire bundle for bridges, the study is conducted on fretting wear during service. First, based on the structure of the parallel steel wire rope, the squeezing forces between the steel wires at different positions caused by the twisting angle and the sheath clamping effect are calculated separately. Then, a contact mechanics model between parallel steel wires is established, and a calculation method for the depth of fretting wear of parallel steel wires is proposed based on the amplitude and frequency of fretting. Finally, the wear depth of parallel steel wire cables in a cable-stayed bridge that has been in service for 20 a is calculated and compared with the measured results.The result shows that (1) the contact mechanics model can accurately calculate the wear depth of wires at different positions of parallel wire rope during service; (2) in the length direction of the cable, the wear degree of the steel wire near the end is greater than that of the middle steel wire, from the section distribution of the cable, the wear degree of the outer steel wire is light, the wear of the steel wire near the center of the circle is serious, and the theoretical calculation results are basically consistent with the detection results of the old cable of the real bridge; (3)the development of steel wire wear depth shows a power function rule of first fast and then slow with the increase of time, the wear rate increases with the increase of contact force between steel wires, vibration frequency and amplitude of cable; (4)the zinc coating of steel wire in the example will be worn out in 4.5 a to 9 a, which is far lower than the failure time of zinc coating caused by environmental corrosion. Fretting wear will lead to premature failure of zinc coating and shorten the initiation time of fatigue crack. If fretting wear between parallel steel wires is not considered, the life evaluation of cable will be unsafe.