Abstract: The glass fiber was exposed to the ultraviolet ray and treated with sulphuric acid,NaOH and NaCl with certain concentrations at certain temperatures respectively,and the tensile strength of the treated fibers was tested.The results show that after the above treatments,a significant decrease of the fiber strength is observed.After 4 hours′ exposure to ultraviolet ray,the fiber strength drops by 50% approximately;2 weeks′ treatment with sulphuric acid solution(0.5%) decreases the fiber strength by 17%;1 week treatment with NaOH solution(2%) results in 33% decline of the fiber strength;and 2 weeks′ treatment with NaCl solution(2%) makes the strength decrease by approximately 7%.The research work is considered to be of reference value in evaluating the strength of glass fiber products.