Abstract: An ultraviolet aging test of ARMOS fiber was carried out with the irradiation of xenon lamp，in which the effects of ultraviolet aging on ARMOS fiber were studied by single fiber tension，FTIR，SEM and XRD. The results show that the tensile strength of ARMOS fiber increases 13.7% after UV irradiation for 6 h and decreases 2.1% after 36 h. The C—N in amide of the ARMOS fiber is broken；hydrogen bond combination ability and crystallinity increase；grooves appear on the surface of ARMOS fiber；the tensile failure mode changes from fibril splitting to brittle fracture by FTIR，SEM and XRD. It could，therefore，be concluded that short time UV irradiation can cause two contradictory effects on the ARMOS fiber.