The invention relates to a glass fiber composition. The composition comprises the following compositions in percentage by weight: 58 to 65 percent of SiO2, 20 TO 26 percent of CaO, 9 to 17 percent of Al2O3, 0.5 to 1 percent of MgO, 0 to 5 percent of B2O3, 0 to 1 percent of F2, 0.1 to 1 percent of TiO2, 0 to 0.8 percent of K2O and Na2O, 0.1 to 0.5 percent of Fe2O3, and 0 to 0.6 percent of SO3. The glass fiber composition uses SiO2-Al2O3-CaO three-element system as basis, introduces MgO and B2O3 with low content, and reasonably designs the gross weight of alkaline metal oxides and the proportional relationship between the MgO and the CaO, not only contributes to the improvement of the mechanical strength, the high temperature resistance and the chemical stability of the glass, but also has excellent drawing performance; furthermore, the glass fiber composition has low cost in raw materials, and meets the requirement of environmental protection.