Abstract: In order to understand the exploitation status of largehead hairtail (Trichiurus japonicus) fisheries in the Sea of Japan and the East China Sea, we used a fishery assessment model based on abundance index (Abundance maximum sustainable yields, AMSY) to assess the two fisheries. The results show that during most of the 1990s and 2000s, the relative biomass levels (B/B_MSY) of the largehead hairtail fisheries in the two seas were lower than 1, but the relative fishing mortality levels (F/F_MSY) were higher than 1, which indicates an overfished state. The estimated parameters such as relative maximum sustainable yield (MSY_q) and relative fishing mortality at MSY level (F_MSY) of the AMSY model were more sensitive to different prior distribution ranges of intrinsic rate of increase (r), while the estimated biological reference points (BRPs), i.e., F/F_MSY and B/B_MSY were more sensitive to the lower limit of different prior distribution ranges of relative biomass level (B_t/k). AMSY can estimate the BRPs of the target fisheries under MSY framework using only catch per unit effort (CPUE) data, prior information of r and relative biomass level for a specific year. AMSY is appropriate for fishery stock assessment in the sea areas where lack statistical data of catches.