Sea turtles are a key group among globally endangered and threatened species （ETPs）， holding significant ecological importance and conservation value.To investigate the species composition， influencing factors of bycatch abundance， and interannual variation of sea turtle bycatch in the tuna purse seine fishery of the Western and Central Pacific Ocean （WCPO）， this study utilized data from the Western and Central Pacific Fisheries Commission （WCPFC） Regional Observer Programme （ROP） from 2013 to 2019. Generalized Additive Models （GAMs） were applied to standardize the bycatch per unit effort （BPUE） for major sea turtle species. The results identified four primary bycaught species：green turtle （Chelonia mydas）， olive ridley turtle （Lepidochelys olivacea）， loggerhead turtle （Caretta caretta）， and hawksbill turtle （Eretmochelys imbricata）， which together accounted for over 90% of total bycatch. The GAM results indicated that the contributions of environmental and spatiotemporal variables varied among species. Sea surface temperature （SST） was a key driver of BPUE for both olive ridley and green turtles， while longitude （LON） was a significant variable （P<0.05） in all models. Standardized BPUE values were higher than nominal BPUE， though their trends were generally similar across most years. From 2015 to 2019， BPUE declined continuously for olive ridley， hawksbill， and loggerhead turtles， whereas it increased for green turtles. This study enhances understanding of the mechanisms driving sea turtle bycatch in purse seine fisheries and provides a scientific basis for future risk assessments and the development of targeted mitigation strategies.