The biological activity, mass transfer effect of the particles and the structural distribution and synergistic relationship of the internal flora are affected by the culture substrate and particle size of the granular sludge, thus determining the effluent quality.The aerobic granules were successfully treated in the SBR reactor for 185 days using the tomato paste processing wastewater as a substrate.The particles of four sizes were sieved for simultaneous batch experiments to examine the sludge characteristics and the decontamination efficiency of the tomato paste processing wastewater. The results showed that the particle of 0.45~1 mm is irregular in shape and the surface porosity is small; 1~1.6mm and 1.6~2 mm tend to be spherical and ellipsoidal, with a smooth surface and dense structure; Although there are more surface gullies and pores in the 2~8 mm, the stability of the system could be maintained well. The presence of pores may provide conditions for the transport of internal materials and the excretion of microbial metabolites within the particles. The average sedimentation rate and specific gravity are positively correlated with the granule size; the water content is negatively correlated with the particle size, which greatly reduced the production of excess sludge. Compared with the granular sludge of 1~1.6 mm, 1.6~2 mm, 0.45~1 mm and 2~8 mm, the latter two particles have better ability to degrade organic matter, and the removal rates of COD are 97.8% and 94.2%, respectively; 1.6~2mm has the best degradation effect on NH4 -N and PO43--P, with the removal rates of 92.7% and 99%, respectively. The removal effect of 0.45~1 mm granular sludge on PO43--P is 69%.