Abstract: The absorption of atmospheric aerosol particle affects earth's radiation balance and laser transmission in atmosphere, especially high energy laser. The precise measurement of aerosol light absorption is paid more and more attention. The basic principles of the photo-thermal interferometry for measuring aerosol absorption coefficient, demodulation algorithms and calibration principle were introduced. A fiber structure photo-thermal interferometer instrument was developed, and the feasibility was verified by measuring the absorption of N2, NO2 and black carbon aerosol. Finally, quantitative analysis was executed with the standard NO2 gas at 532 nm whose detection limitation was 3.976 mgm-3. The qualitative and quantitative analysis demonstrate that the fiber structure photo-thermal interferometer has great potential in practical aerosol absorption measurement.