Abstract: Unraveling the phylogeographical history of the species stands as a key endeavor for comprehending the evolution of the rich biodiversity and high endemism found in East Asia. Here we recovered the phylogeographical patterns and demographic histories of three East Asian endemic fishfly and dobsonfly species of the holometabolan order Megaloptera (Neochauliodes formosanus, Protohermes costalis, and Neoneuromus orientalis), with a broad and largely overlapped distribution, based on comprehensive mitogenomic data. We found a consistent impact of vicariance on the population isolation of Neo. formosanus and P. costalis between Hainan, Taiwan, and the East Asian mainland during the early Pleistocene, potentially impeding the subsequent colonization of the later diverged Neon. orientalis to these islands. We further unveiled the dual role of the major mountains in the East Asian mainland serving as both barriers and conduits in shaping the population structure of all three species. Notably, we demonstrated that these co-distributed species originated respectively from Southwest, Southern or eastern Central China, and subsequently migrated along multi-directional routes, forming their sympatric distribution in the East Asian mainland. Our results also underscore the significance of Pleistocene land bridges along the eastern coast of East Asia, particularly in facilitating the dispersal of insects with mountain-dwelling habit and low dispersal ability. This study provides novel insight into the synergistic impact of Pleistocene geological and climatic events on the diversity and distribution of aquatic insects from East Asia.