Tridrepana marginata is a moth in the Drepanidae family. It was described by Watson in 1957. It is found in China (Yunnan). The wingspan is 27-32.2 mm for males and 30.2-39 mm for females. This shape of the forewings is unusual, the terminal half of the costa is strongly bowed inwards and the apex is not strongly falcate but the outer margin below it is deeply concave and then distinctly arched. There is an orange shadow on the forewings, extending from the apex to the outer one third of the inner margin. There are also two white patches ringed by brown lines.