Echoes from two targets cannot be distinguished if two targets are located in the same range. This will cause an error in some analysis process such as analysis to estimate fish density. Therefore, a high quality of single echo detection (SED) is needed to minimalize the overlapping echo. The aim of this study is to estimate target strength and density of the fish / stock using different SED criteria using split beam echo sounder in Pari Island. Data processing used was Sonar5-pro software for SED measurement. Data processing stages were producing new SED-echogram and executing biomass analysis using Sv/TS Scaling method. SED criteria setting are SED-ori, SED-d, SED-f, and SED-m. Using different SED criteria in biomass analysis produces different target strength and density of fish. Number of single fish detection and fish size proportion in each SED criteria setting is different. Distribution of Target Strength (TS) is dominated by -70 dB to -61 dB, fish length 0,8-2,2 cm, and density 1.000-5.000 fish/ha. The suggested SED criteria are SED-f for a high accuracy measurement.