Abstract: Purpleback flying squid (Sthenoteuthis oualaniensis) is a typical epipelagic economic cephalopod in the South China Sea. It plays a crucial role in the matter cycle of marine food webs. We collected 929 specimens from 22 stations in the southern South China Sea during 2016–2017, and measured 19 morphological traits. We applied analysis of variance (ANOVA), principal component analysis (PCA), coefficients of variation (CV), and regression analysis to evaluate sexual differences, spatial variation, and their relationships with environmental factors. The results showed significant sexual differences in six traits, including mantle length, arm lengths, fin dimensions, body mass, stomach mass, and gonadal mass (p<0.01). Females exhibited greater energy storage and more reproductive investment compared to males. Maturity affected body mass, gonadal mass, head mass, and total stomach mass and other related traits. Spatially, female gonadal mass and male stomach mass exhibited the greatest variability. Regression analyses reveal that salinity and current velocity played dominant roles in shaping function traits. Salinity had significant negative effects on beak-related parameters, whereas current velocity was positively correlated with certain arm lengths (p<0.05), indicating that key environmental factors played dominant roles in shaping functional traits. Overall, this study elucidates the ecological adaptation of S. oualaniensis to complex environmental conditions, and provides fundamental data for cephalopods resource assessment and management in the South China Sea.