In order to study the particle size distribution and sedimentation performanee of domestic sewage, a particle analyzer was used to measure the particle size distribution of influent of three typical domestic sewage treatment plants. The change of particle size distribution and sedimentation performance were compared by sedimentation experiment. The effect of grit setting on particles removal was analyzed. The basic characteristics of particle size distribution and the general rules of sedimentation in typical domestic sewage were obtained. The results show that the median diameter of particles in the influent is 8~14 μm, but decreases to 4~8 μm after sedimentation. The total number of particles does not decrease, but the particle size decreases. The median diameter of particles after grit setting is 9~15 μm, but decreases to 4~12 μm after sedimentation. According to the particle size distribution before and after grit setting, grit setting has no significant removal effect on particles with particle size less than 50 μm.