Integration threshold is the critical signal level that governs whether or not an echo signal will be included in the echo integration during the post-processing of fisheries acoustic data. It is the Volume Backscattering Strength (VBS) of the weakest echo signal that will be involved in the echo integration process. An appropriate integration threshold may effectively remove noise and non-target signals while keep the signals from target species intact, thus improve the accuracy of acoustic estimation of fishery resources. In order to study the methods for the selection and optimization of the integration threshold for a scattered target distribution, the functional relationship between the VBS and the Target Strength (TS) was derived based on basic concepts and formulas in fisheries acoustics, and two methods, namely the TS-Length empirical relationship method and the in situ TS data method, were proposed for the determination of integration threshold. The application of both methods was then demonstrated in the anchovy Engraulis japonicus survey in the Yellow Sea. It provides an effective reference for the definition and optimization of integration threshold in the post-processing of fishery acoustic data with the scattered target distribution.