Based on the near-forward light scattering method, the polydispersion sub-micron aerosol concentration measurement is realized. The tungsten halogen lamp is employed as the light source in the measurement device. The shaped annular beam is converged to the gas to be measured. After being collected by a lens, the scattering light is detected by a photodetector. The aerosol concentration is inversed by analyzing the intensity variation of the detected light. The experimental results show that the detection sensitivity of the measurement method can reach to 10-4 μg·L-1 and the linear response range covers 6 orders of magnitude. This mothod can be applied to the fields of nuclear industry, medicine, microelectronics, and so on.