In order to understand the grain-size structure characteristics of fish communities in Daya Bay, we constructed the biomass particle-size spectrum of fish in Daya Bay based on the data from two bottom trawl surveys in 2016. The heterogeneity of the characteristic parameters of the fish biomass particle-size spectrum from different parts of the bay in two seasons was compared and analyzed. The results showed that the pattern of the Sheldon-type biomass particle-size spectrum of fish in Daya Bay was unimodal; the fish particle size ranged from -2 to 10 and the highest peak was at a grain size of 3-4. The reduction in the curvature of the biomass particle-size spectrum of fish was mainly caused by the reduced size range from the emergence of a small number of large perennial settlers, , and seasonal migratory fish, . From the three areas of the bay (coastal, central, and bayou), the curvatures in the spring were the largest in the coastal area, followed by the central area, and they were the smallest in the bayou. The curvatures in autumn were the largest in the bayou, followed by the coastal area, and they were the smallest in the central area of the bay. The decrease in the curvature of the coastal area was mainly caused by the presence of a large number of small particle juveniles. The decrease in the curvature of the central area was due to the emergence of a small number of large , which reduced the size range. The increase in the curvature in the bayou was mainly caused by the emergence of a small number of large . It can be seen that the number of supplemental groups such perennial settler fish, migratory fish, and perennial juveniles, and the size ranges have a significant impact on the peak shape and curvature of the fish biomass particle-size spectrum. The ABC curve showed that the biomass particle-size spectrum of fish in spring and autumn were in a seriously disturbed state.