In order to understand the optical properties of the colored iceland crystals after fading by heat treatment, the fading conditions are explored by choosing the yellow and the purple crystals. One colored crystal is divided into two parts - the faded and the colored, and the two parts are polished. The optical properties including transmittance, extinction ratio and principal refractive index are measured. The results indicate that the fading temperatures of yellow and purple iceland crystals are 405 ℃ and 485 ℃ respectively (constant temperature for 4 h). The extinction ratio and principal refractive index do not change after fading. The transmission spectra of the purple, dark yellow, light yellow crystals are extended to ultraviolet. Especially for the dark yellow crystal, the transmission range is extended to ultraviolet by about 130 nm, and the transmittance in 400~600 nm is greatly increased. After fading, the optical properties of colored iceland crystal achieve the optical performance of the natural clear crystal. Thus, the colour fading of iceland crystal has great significance for utilizing the scarce natural iceland crystals.