Aerosol time-of-flight mass spectrometer (ATOFMS) is used to measure the refractive index of aerosol particles. First of all, diameter and light scattering intensity of aerosol particles are measured through the self-developed ATOFMS. Then the function relation of theoretical luminous flux accepted by photo multiplier tube (PMT) with aerosol particles size and the refractive index is deduced through the Mie scattering theory combined with the ATOFMS geometric model of light scattering experiment. The refractive index is retrieved by comparing the experimental aerosol particles average light scattering intensity with Mie scattering theory. The result shows that the method is reasonable compared with the actual sample data parameters.