The super-resolution micro-fabrication technique based on the optical absorption modulation of azo-material is attracting attentions for decades. To reveal the mechanism of the optical absorbance modulation of azo-material, the simulations of the variation of absorptivity with time are implemented based on the optical absorption model and the photo-isomerization principles of azo-material. Some membrane samples with different thicknesses are obtained by using a typical azobenzene dye [disperse yellow 7 (DY7)], and the experiment to study the variation of absorptivity with time of these samples is implemented, with 365 nm illumination only and 365 nm and 532 nm illumination together, respectively. The results indicate that the obsorptivity of azobenzene at 365 nm varies significantly due to the photo-isomerization of azobenzene, and it is influnced by the thermal effect due to 532 nm illumination.