A theoretical measurement model of atmospheric particulate concentration is built, considering Mie scattering theory and laser propagation equation. An experimental device is designed to monitor the real-time PM 2.5 concentration is introduced by using a charge- coupled device (CCD) backward scattering lidar. The experimental system consists of a 532 nm wavelength laser as the light source and a CCD as detector of back scattering light. According to the real time image captured by the CCD, the gray level value matrix is extracted, while the intensity distribution of the scattering image is analyzed. Compared with the results of a PM 2.5 monitor for Thermo Fisher Scientific Company, five formulas about PM 2.5 concentration and scattering lighting are concluded with a fitting degree better than 0.95. A further popularization of this atmospheric particulate concentration monitoring device which is low in cost and convenient in use, will play a significant role in investigating the movement of PM 2.5 and depicting pollutant distribution.