The beak was one of the most important hard tissues of cephalopods which was widely used in the study of cephalopod fisheries biology and fishery ecology research. According to the measurement of the morphological parameters of the beak from 818 Sthenoteuthis oualaniensis samples collected by Chinese falling-net fishery during January to March of 2017 and 2018 in the Xisha Islands waters of the South China Sea, the morphological growth characteristic of the beak of S.oualaniensis was studied. The principal component analysis showed that the upper hood length (UHL), the upper crest length (UCL), the upper wing length (UWL), the upper lateral wall length (ULWL), the lower hood length (LHL), the lower crest length (LCL),the lower wing length (LWL) and the lower lateral wall length (LLWL) could be used as themorphological characteristic parameters to study the morphological changes of the beak. The analysis of covariance (ANCOVA) showed that there were significant differences in the relationships between UHL, LWL versus mantel length (ML) between males and females, but no significant difference was found in other characteristic parameters. The relationships between beak morphological variables and body weight (BW) differed significantly between males and females in all of the morphological characteristic parameters. The relationships between LLWL,UHLof males and ML were optimally described by the linear growth models, and exponential functions were optimal for the other parameters. The logarithmic functions were optimal for the relationship between the ULWL, LHL, LCL, LWL, LLWL and BW for females, however exponential equations were optimal for the UCL,UWL, and linear functions were optimal for the other parameters for males.