Abstract: To explore the growth characteristics of Sthenoteuthis oualaniensis, the morphological characters of gladius structure were studied based on the 594 samples collected in the northwest Indian Ocean in autumn of 2019 (September to November). Principal component analysis showed that gladius length (GL), cones length (CL), vanes length (VL), greatest width of cones (GWC) and greatest width of proostracum (GWP) could be used as characteristic parameters to describe the change of the gladius shapes. Results of the analysis of covariance (ANCOVA) showed that there were significant differences between sexes in the growth relationship between all characteristic parameters and mantel length (ML) except VL, and there were significant differences between sexes in the growth relationship between all characteristic parameters and body weight (BW). According to equation fitting and Akaike′s Information Criterion(AIC) analysis, the relationship between VL and ML was most suitable for the linear function expression, GL, CL and GWP were most suitable for linear functions, and GWC was most suitable for the power function. The relationship between CL and BW of males was best expressed by the linear function, GL was best expressed by the power function, and GWC, GWP were best expressed by logarithmic functions. The relationship between all characteristic parameters and BW of females were best expressed by the power functions, the relationships between GL, VL and BW of males were most suitable for the power functions, CL was most suitable for linear function representation, GWC and GWP were most suitable for logarithmic function representation. The determination of the optimal fitting function of the relationship using gladius structure between the characteristic parameters and ML and BW can provide a reference for fishery biology and resource assessment of S. oualaniensis.