NDIR is one of the important NO2 concentration measurement methods. The NO2 concentration can be figured out through measuring the light intensity attenuation. But the scattering and absorption of the multidispersion soot particles can attenuate the light intensity, so the infrared measurement light intensity attenuation is larger and the concentration is increased. The interference on the NO2 concentration caused by the multidispersion soot particles is discussed in the paper. The dissipativity, concentration, average size, size distribution parameters and the scattering light angle range of the multidispersion soot particles can interference the NO2 concentration. The method to reduce the interference is brought out and the NO2 concentration measurement accuracy is improved.