In order to analyse the inter-annual variation in the population structure and composition of the purpleback flying squid （Sthenoteuthis oualaniensis） and its main environmental influences. A productive fishery survery was conducted on two consecutive cruises from December 2019-February 2020 and September-November 2020 in the open ocean waters of the northwestern Indian Ocean from 60°E to 65°E, 15°N to 20°N, to collect samples of the Indian Ocean purpleback flying squid was carried. During the survey, we obtained 1 430 purpleback flying squid samples, with a total of 748 sexes identified, and a total sex ratio of male to female of 1∶0.97.We analyzed the biological characteristics of the purpleback flying squid, like mantle length, body mass, sex, sexual maturity and feeding intensity, by means of the SPSS statistical software. The average mantle lengths of females and males were 248 mm and 207 mm, respectively, and the dominant mantle length group was 220-250 mm. The Logistic curve was employed to fit the mantle length at the first sexual maturity of the purpleback flying squid. During the first voyage, the mantle length at the first sexual maturity for female individuals reached 361 mm, while that for male individuals was 171 mm. In the second voyage, the mantle length at the first sexual maturity of female individuals measured 202 mm, and that of male individuals was 153 mm. The proportion of individuals with gonadal maturity stages Ⅲ, Ⅳ and Ⅴ （sexual maturity） was as high as 66.53 %, with 57.37 % of females and 75.20 % of males in the mature group. Meanwhile,by utilizing the marine environmental data acquired from remote sensing satellites, the relationship between the distribution of the proportion of mature groups of purpleback flying squid and the main environmental factors was analyzed. It was considered that their growth and development were influenced by crucial factors in the marine environment, namely sea surface temperature （SST）, sea surface temperature anomaly （SSTA）, chlorophyll-a mass concentration （Chl.a）, and so on.In addition, the survey showed that the proportion of sexually mature groups of purpleback flying squid was 25.93% higher in the December 2019-February 2020 cruise compared to the September-November 2020 cruise. The above conclusions provided a reference basis for the later sustainable development and utilization of purpleback flying squid resources in the northwestern Indian Ocean waters.