【目的】 扁刺蛾Thosea sinensis是茶叶重要害虫，本研究拟建立一种快速鉴别扁刺蛾蛹和成虫性别的简易方法，可为该虫的野外种群监测及预测预报提供更精准的数据。【方法】 利用体视显微镜观察、拍照记录扁刺蛾不同虫态形态特征，比较分析蛹、成虫雌雄的体征差异，通过成虫外生殖器特征验证性别鉴定结果。【结果】 扁刺蛾雌蛹生殖孔位于第8腹节，产卵孔位于第9腹节，生殖孔和产卵孔周围平坦无突起；但是雄蛹生殖孔位于第9腹节，呈现纵裂缝状，且两侧各有一半圆形瘤状突起。雌成虫触角丝状，腹部末端圆筒状，轻轻按压腹部，即可发现其生殖器官产卵瓣为扁椭圆形；但是雄成虫触角栉齿状，且触角长度显著短于雌成虫触角，腹部末端较细，生殖器官抱握器呈钳状。该方法能快速鉴别扁刺蛾蛹及成虫的性别，其准确率为100%。【结论】 通过确定扁刺蛾蛹生殖孔位置及其形态，可以准确区分雌、雄蛹，通过辨识其成虫触角，或轻压腹部观察其生殖器结构可准确区分成虫性别。

 [Aim]  Thosea sinensis is an important pest of tea. A simple quick and accurate method was developed to sex pupae and adults of T. sinensis to provide more accurate data for field population monitoring and prediction of this insect. [Methods]  The morphological characteristics of pupae and adult of T. sinensis were observed and compared. Adult genital types were used to validate the results of sexing. [Results]  The reproductive pore in female pupae is located on the 8th ventral segment and the oviposition hole is on the 9th ventral segment. The surroundings of these two holes are flat with no protrusions. The reproductive pore is on the 9th ventral segment and is characterized by a longitudinal crack shape. In male pupae there are semi-circular tumor-like protrusions on both sides of the reproductive pore. In female adults, the antennae are filamentous, and the end of the abdomen is cylindrical. Pressing the abdomen gently reveals that the oviposition valve is flat and oval. The antennae of male adults are comb-toothed, and the length of antennae is significantly shorter than that of adult females. In adult males, the end of the abdomen is thinner, and their reproductive organs feature a pincer-shaped grasper. The method can quickly identify the sex of adult and pupae of T. sinensis with 100% accuracy. [Conclusion]  Male and female T. sinensis pupae can be accurately distinguished by determining the position and shape of the reproductive pore. The sex of the adults can be accurately distinguished by observing the antennae or the genital structure by lightly pressing the abdomen.