Abstract: As a typical aggregating marine organism, aggregation characteristics of Antarctic krill (Euphausia superba) is an important part of behavioral ecology researches. Antarctic krill are distributed around the South Shetland Islands with high density. The mechanistic explanations of the shape and size of Antarctic krill aggregation remain controversial. The acoustic data of Simrad EK80 collected from the water around the South Shetland Islands were analyzed using Echoview V6.16. Antarctic krill aggregations were classified into 13 types. The effects of environmental (sea surface temperature and sea condition) and spatialtemporal variables on aggregation type were examined by principal coordinate analysis (PCoA). The results showed that sea condition (wave) was the most important fact affecting the aggregation type of Antarctic krill, followed by the illumination intensity. Patched smallsized aggregation had a wide distribution at the spatialtemporal level, with higher proportion both at night and daytime (>30%). Smallsized aggregation often occurred during the daytime, whereas largesized aggregation occurred at night. Krill aggregation in February was significantly associated with sea condition and latitude, significantly associated with brightness in March, and significantly associated with both brightness and sea condition in April.