Aiming at the problem of deviation in measurement results caused by background interference when using CMOS sensor static light scattering method to measure particle size, this paper proposes a background interference elimination method based on the baseline method, and uses 120 μm and 9.86 μm national standard samples for the experimental analysis. The experimental results show that the baseline method can effectively reduce the deviation in measurement results caused by background interference, which provides a technical reference for the use of CMOS sensor to carry out an accurate particle size measurement of suspended particles in water body by static light scattering.