The photothermal effect and thermal induced photorefraction change of aerosols in the atmosphere were researched. The method to improve detection sensitivity by increasing the number of photothermal effect zones and to reduce the costs by low coherence interferometry was proposed. A mathematics model to measure the aerosol absorption coefficients by photothermal low coherent interferomtry was established, the detection sensitivities from two ways, interferometric orthogonal measurement and interferometric fringe subdividing detecting, were analyzed, and the detecting limit in low coherent polarized interferometry was discussed. Experiments demonstrate that the detection sensitivity in theory can be 1×10-6 m-1. If a longer interaction length and more number interaction zones are choosen, higher sensitivity can be arrived. The theory and method proposed in this paper can provide references for aerosol measurements.