In order to explore the influence of the division of different intervals of Trachurus japonicuson on its population parameters and stock assessment, the length frequency with the data of the fork length of T.japonicus in the Beibu Gulf from 2006 to 2018 was reconstructed, and logistic curve fitting and length Bayesian biomass estimation method (LBB)were used to estimate the first sexual maturity fork length (L₅₀), asymptotic fork length (L_∞),relative natural mortality (M/k),relative fishing mortality (F/k), total mortality (Z/k), optimal fork length-at-first-capture (L_{c_opt}), exploitation rate (E) and other population parameters. The differences in population parameters under different intervals.The results show:The fork length of first sexual maturity ranges from 157 mm to162 mm; The average values of L_∞, M/k, F/k, Z/k, and L_{c_opt} of T. japonicusin intervals length are 248 mm, 1.38, 6.92, 8.28, and 156 mm, respectively; The relative biomass B/B₀ is less than 0.5, and E is greater than 0.5; The results of population parameters estimated by reconstruction length frequency of intervals are different, and the fluctuations are more obvious with the increase of intervals.Studies have shown that the biomass of T. japonicus is relatively low and is in an over-exploited state. At the same time, it is recommended to determine the length of a certain fish interval based on the number of samples, length composition and biological characteristics.