Antarctic krill () is a key species in the Southern Ocean ecosystem, and knowledge regarding its biomass is essential to understand the ecology and distribution of krill. The acoustic data was collected across extensive gradients in the South Orkney Islands on the commercial fishing vessel . Krill targets were identified in acoustic data using a multi-frequency identification window and converted to krill density using the Stochastic Distorted-Wave Born Approximation target strength model. The average krill length was (33.01±4.06) mm, with a maximum length of 49.21 mm and a minimum length of 25.50 mm. There was no significant difference between male and female krill length. The whole ecogram could be divided into 1338 integration units, of which 586 units were in daytime and 752 units were at night. The maximum krill density was 554.07 g/m² and the minimum density was 0 g/m². The Antarctic krill were mainly aggregated, with 87.90% integration units having no biomass. There was no significant difference in diurnal NASC and values of the 9 transects, which suggested that the diurnal vertical movement had no effect on the estimation of krill biomass. The average krill density was 71.01 g/m² and the total biomass was 1.77×10⁶ t in this area. The krill were mainly aggregated in a 60-180 m water depth range in the daytime, and gradually moved upwards or downwards at night. Light intensity is one of the factors that influence the krill diurnal vertical movement. However, a proportion of the Antarctic krill sunk to deeper waters at night, which may be to prey on the deep-water food. The results of this study provide abundant information on krill distribution in this area and basic data for current feedback on the krill resource management of CCAMLR. In future, the research on the correlation between krill biomass and external factors (environmental factors, predators) can help us understand the population structures more accurately and predict the distribution of krill resources.