Z_scan experiments are performed on the azobenzene polymer (DR_13_PMMA) films with He_Ne laser. It is found that the relation between the cha nge of refractive index of the sample and the light intensity behaves like a sat u rable effect, whose relative parameters are alterable with light intensity. It i s also found that the change of refractive index induced by linearly polarized l ight is distinctly greater than that induced by circularly polarized light. The phenomena are explained by using the theory based on the effect of angular hole burning of photoisomerization.