The diameter distribution of high-strength glass fiber (HS2) strands and rovings was analyzed, and the influences of the average fiber diameter and the diameter distribution on the mechanical properties of HS2 glass fibers were evaluated. The results show that the tensile strength of fiber bundles and impregnated rovings decreases with the increase of the diameter when the diameter is >11μm. The tensile strength of unidirection orientated fiber reinforced plastic plates with the fiber diameters of 11-13 μm is not affected by the diameter, and the shear strength decreases with the increase of the diameter. The wide distribution and high variation coefficient (Cv) have an adverse effect on the mechanical properties of the fiber. When the average fiber diameter is 11μm, the roving tensile strength of the diameter with Cv 0.20 is 8% lower than that with Cv 0.15. The diameter distribution can reveal the forming tooling and process, and the process needs to be strictly controlled to refine the highly uniform fibers.