Photo-thermal interferometry, which is highly sensitive, real-time and free-effected by light scattering, can directly measure the absorption coefficient without changing atmospheric aerosol state. It is firstly elaborated that the basic principles of photo-thermal interferometry for measuring aerosol absorption coefficient. Several typical photo-thermal interferometers are analyzed, including Mach-Zehnder interferometer, Fabry-Perot interferometer, Jamin interferometer and folded Jamin interferometer. Then the research process of this method and corresponding unsolved problems are brought out. On this basis, a fiber structure photo-thermal interferometer test device is developed. Finally, the future trend of this method is concluded.