In recent years, haze phenomenon is becoming more and more serious in China. It not only harms people’s health and air traffic caused by security risks, but also affects a lot of optics equipment used outdoor. In order to quantitatively analyze the effect of different haze levels on the performance of the trace gas concentration detection system based on the elastic light modulator, the test system was designed. The effect of different PM2.5 concentration sample gas on the inversion of equivalent VOC gas concentration was quantitatively analyzed. In the experiment, different concentrations of PM2.5 were collected in the field, and then mixed with the standard gas to be prepared. Finally, the comparison of the transmitted light spectrum and the measured gas concentration inversion data was made. The effect of PM2.5 concentration on the system was quantitatively analyzed. In the experiment, formaldehyde and benzene were used as the gas to be measured. Six kinds of concentrations of the gas to be measured were prepared, and 6 haze concentration levels (from No. 1 to No. 6) were tested. The experimental results showed that when the PM2.5 concentration increases, the system light energy absorption rate is significantly reduced. When the PM2.5 concentration level is less than No.3, the attenuation change is relatively slower, and when it is greater than No.3, the attenuation effect is enhanced. When the PM2.5 concentration is less than 150 g·m-3, the test accuracy is better than 90%; When the concentration of PM2.5 exceeds 150 g·m-3, the effect of inversion of VOC concentration becomes stronger. When 350 g·m-3 is reached, the test error is nearly 30%. It can be seen that PM2.5 concentration has a significant effect on the gas concentration detection of the optical modulation system.