The change process of optical properties in As-S films with different compositions during exposure to Ar+ laser light is studied. The experimental results show that photo-induced change of the optical properties of As2S3 film is the largest, and is a volume effect. The kinetics of the structure change is discussed. The change behaviour of the refractive index in newly deposited As2 S3 film under the cycles of annealing-exposure is also studied, reversible change of refractive index is about 0.03, and the irreversible about 0.1.