More than 100 Hemeroscopid larva fossils were discovered from the Lower Cretaceous in Southwest Beijing, which effectively ends the discussion of morphology and makes it more complete. It is assigned within the Libellu-loidea, and shows close evolutionary correlations with modern Libellulidae. Although the wing characters of adult Hemeroscopus from the same formation indicates the close relationship to Aeschnoidea, we suggest that the larvae and the adults were the same species. Therefore, it probably shows the evolutionary ancestors of Libellulidae. Being the fundamental species discriminating Jehol Entomofauna and Lushangfen Entomofauna, Hemeroscopus bears great significance in the study of stratigraphy. More than 100 Hemeroscopid larva fossils were discovered from the Lower Cretaceous in Southwest Beijing, which effectively ends the discussion of morphology and makes it more complete. It is assigned within the Libellu-loidea, and shows close evolutionary correlations with modern Libellulidae. Although the wing characters of adult Hemeroscopus from the same formation indicates the close relationship to Aeschnoidea, we suggest that the larvae and the adults were the same species. Therefore, it probably shows the evolutionary ancestors of Libellulidae. Being the fundamental species discriminating Jehol Entomofauna and Lushangfen Entomofauna, Hemeroscopus bears great significance in the study of stratigraphy.