[Aim]  To investigate the influence of nest-building time, emergence time and other factors, on the offspring sex ratio of the wasp Anterhynchium flavomarginatum in the Guizhou Chishui Cyathea Reserve . [Methods]  A. flavomarginatum were captured using trap nests in 2023, after which colonies were systematically observed and recorded. The offspring sex ratio and temporal fluctuation in nest numbers were analyzed using the Wilcoxon rank sum test. [Results]  A total of 1 471 nests were observed; 84.5% of the 1 741 solitary wasp nests. Prey were mainly lepidopteran larvae of the Crambidae and Pyralidae families. The offspring sex ratio was highest (2.00) in June and lowest (0.79) in August. The highest number of nests was in October and the lowest in June. The number of male offspring was highest in August, significantly higher than in June (P<0.001), and the number of female offspring was highest in October, significantly higher than in July (P<0.001) and September (P=0.031). The ratio of male to female offspring was highest in nests of 4-8 mm diameter (1.50), and in nests of 16-20 mm nest diameter (0.69). The number of insect cells and the number of males and females in nests with an inner entrance diameter of 8-12 mm were significantly higher than in other nests, and the female to male offspring ratio in such nests was 1.22. [Conclusion]  A. flavomarginatum can adjust its nesting strategy according to the nesting season and the nest tube diameter, and the number of nests and sex ratio of its offspring are significantly affected by nesting time and nest tube diameter. These results provide new insights into the reproductive strategies and ecological adaptations of A. flavomarginatum.