It is difficult to test the transmittance parameters of glass in the form of glass fiber. The transmittance of glass fiber is characterized by the transmittance parameters of glass with the same formula. The transmittance of glass in glass fiber is tested and evaluated by quoting the visible light single-point transmittance T550 nm, infrared light single-point transmittance T940 nm, ultraviolet light single-point transmittance T365 nm and visible light full-band transmittance T380-780 nm. On this basis, the concept of visible light transmittance stability is characterized by ΔT (ΔT=T550 nm -T380-780 nm).