A new kind of quasi-periodic optical microstructure arranged by the Fibonacci sequence is proposed. In the case of TM polarization, the absorptivity of the optical microstructure is calculated numerically based on the rigorous coupled wave analysis (RCWA) method. A parametric study is carried out to evaluate the influences of Fibonacci series duty ratio and the thickness of the coating film on microstructure. Under AM1.5 solar spectral irradiance, when the Fibonacci series is S3, the duty ratio is f=0.7, and the thickness of the coating film is t=20 nm, the maximum averaged absorptivity can reach 95.17% within the wavelength of 300~1100 nm, which suggests that it has great potential to be an anti-reflection layer on the surface of solar cells.