The Relationship between Grains Size of Silver Halide and Photochromism in Photochromic Glass Zhang Xinmin;Ding ZhenyaUsing the line broadening of x-ray diffraction and SAXS, the phase of microcrystalline in photochromic glass is determined, and the grains size of silver halide and its distribution are measured. The relationships between silver halide grains, saturate darkening and fading rate are studied, and linear regression equation is established to describe the relationship. The mechanism of fading is discussed based on the view point of electron proc- ess of photochromism. The results are as follows: 1. The microcrystalline in photochromic glass is Ag (Cl, Br) solid solution. 2. The initial fading rate and saturate darkening is closely correlated with size of silver halide grains. The effect of darkening is greater than that of grains size. Initial fading rate increases with the increase of dark- ening and decrease of grains size for the same system in photochromic glass.