Formation of surface-relief-gratings (SRGs) on amorphous azo glass films (IAC-4) was studied by using two interfering Ar+ laser beams with p+p, p+s and RCP+LCP polarizations to inscribe the gratings. The diffraction efficiencies and the surface modulation of SRGs are measured by real time grating diffraction efficiency detection method and atomic force microscope, which strongly depend on the polarizations of the writing beams and show an order of RCP+LCP>p+s>p+p. SRGs can be rapidly inscribed on IAC-4 films with large surface modulations and high diffraction efficiencies when irradiated with RCP+LCP interfering beams. But the inscription was quite inefficient using p+p interfering beams. When irradiated with p+s polarization beams, formation of half-period gratings was observed. After irradiated with p+p, p+s or RCP+LCP interfering beams (58 mW/cm2 per beam) for 80 s～2 min, the diffraction efficiencies and modulated depths of the photo-induced SRGs are 3.1% and 23 nm, 9.3% and 120 nm, 62% and 734 nm respectively. The results indicate that IAC-4 can be used as a competitive material for SRG applications, but the fabrication heavily relies on the light polarization conditions.