In order to analyze the influence factors of particle size measurement method based on extinction spectroscopy, the experimental system of particle size measurement and the non-linear least square algorithm for particle size extinction spectral inversion was established. The experimental research with particle samples using three kinds of standard particles (900 nm, 2.1 μm and 5.1 μm) was carried out under the different wave band range, wavelength selection number and particle concentration. The results show that the selection of parameters such as wavelength range, wavelength number and particle concentration has non-negligible influence on inversion accuracy of particle size of extinction spectroscopy. The SNR (signal-to-noise ratio) of extinction spectrum is the important indicator for the selection of wavelength range. There is a threshold value of wavelength selection number. When the threshold value is used, the measurement accuracy can be ensured, but also the decrease of inversion calculation speed which due to the lengthy spectral data can be avoided. The extinction value of measured particle system about 0.75 is optimized for inversion of particle size.