Abstract: Starting with core-sheath composite fibers into which some photosensitizer has been mixed, weak acidic composite ion-exchange fibers are produced by pre-irradiation grafting in the presence of oxygen. The influence of absorption dose, reaction temperature, inhibitor and photosensitizer on the grafting degree is investigated. The results show that the grafting degree increases with the increase in the absorption dose, and up to 1 600% is attainable. In the plots of grafting degree against temperature and against inhibitor concentration, a maximum is observed. An optimal temperature of≈70 ℃ and (a best) concentration of the inhibitor of 0.25%(mass fraction) are deduced. The addition of some photosensitizer significantly depresses the necessary absorption dose. The more the photosensitizer is added, the more remarkable the sensitization effect will be.