Sea turtles are at the top of the marine ecosystem and have been regulating the diversity and stability of marine ecosystems. Based on the data by scientific observer surveys in high seas of the tropical Atlantic Ocean (15°S-15°N, 15°W-45°W) by the pelagic tuna longline fishery targeting bigeye tuna from 2009 to 2019, the total 108 sea turtles were observed and analyzed.The result showed that incidental sea turtles were classified as 3 species, namely loggerhead (Caretta caretta), olive ridley turtle (Lepidochelys olivacea) and leatherback (Dermochelys coriacea). There were 32 sea turtles of mortality after capture. The annual catch rate ranged from 0.001 6 per thousand hooks to 0.069 3 per thousand hooks. And the interactions between fishing gear and sea turtles showed that most sea turtles bycatch in longline are caused by hooked mouth and branch line entanglement.Seasonal differences were found in sea turtles bycatch,and BPUE(bycatch per unit effort)occurred mainly from October to May in next year. BPUE in the north of the equator exhibited interannual variations, but the overall extents were not large. However,in the south of the equator,BPUE varied greatly, even in some years there were no bycatch reports,especially from 2009 to 2013. However, since 2013, the growth trend of BPUE in southern area appeared obviously, and the maximum value occurred in 2015, then southern BPUE gradually decreased to the minimum value in 2019.There was a great difference in BPUE between the bright moonlight and moonless night, especially at full moon or near full moon, the BPUE increased significantly. Different species of bycatch sea turtles occurred in a certain temperature range. Leatherback turtles were more often caught when the water temperature ranged from 24 to 26℃, while olive ridley turtles were easier incidentally caught between 26 and 27℃. In addition, this research explored the factors affecting the increase of sea turtles bycatch survival rates about Chinese longline fleet in recent years, and suggestion was also made to adjust the management plan of sea turtles bycatch mitigation in high seas of the tropical Atlantic Ocean in real time according to the difference of fishery area, target species and environmental conditions.