Sthenoteuthis oualaniensis in the open waters of South China Sea, two acoustical surveys were conducted using scientific echosounder (Simrad EY60) in the area of central and southern South China Sea (16°–5°N) in the autumn in 2012 and the spring in 2013. The survey results showed: (1) in the autumn in 2012 were 3.26×10¹⁰ inds and 2.14×10⁶ t respectively and the coefficient of variation was 23%; the mangle length range, mean mantle length and mean body mass of were 62, 127 mm and 65 g, respectively; in the autumn population distributed in the entire central and southern South China Sea, mainly distributed north of 8.0°N and 114.0°E area; the maximum abundance density and biomass density of (6.5°N, 111.0°–111.1°E) and 85 t·nmi^–2 (15.0°N, 114.35°S. oualaniensis in the spring in 2013 were 2.98×10¹⁰ inds and 2.44×10⁶ t respectively and coefficient of variation was 23%; the mangle length range, mean mantle length and mean body mass of Sthenoteuthis oualaniensis were 73, 122 mm and 82 g respectively; in the spring population also distributed in the entire central and southern South China Sea, mainly distributed north of 11.0°N area; the maximum abundance density and biomass density of (13.0°N, 116.55°115.35°E) respectively. The research results indicated that the biomass of t in the open water of South China Sea; compared with the autumn in 2012, concentrated ground of moved north and east in the spring in 2013.