This study investigated the influences of geographic isolation and climate fluctuation on the genetic diversity, speciation, and biogeography of the genus Pseudovelia (Hemiptera: Veliidae) in subtropical China and tropic Indo-China Peninsula. Species nucleotide and haplotype diversities decreased with reduction in species distribution limits. The gene tree was congruent with the taxonomy of monophyly, except for four species, P. contorta, P. extensa, P. tibialis tibialis, and P. vittiformis. The conflicts between the genes and species tree could be due to long-term isolation and incomplete lineage sorting. Diversification analysis showed that the diversification rate (0.08 sp/My shifted to 0.5 sp/My) changed at 2.1 Ma, which occurred in the early Pleistocene period. Ancestral area reconstruction suggested that subtropical species possibly evolved from the tropics region (i.e., Indo-China Peninsula). Results implied that narrow endemics harbored relatively low genetic diversity because of small effective population and genetic drift. Radiation of subtropical Pseudovelia species was rapidly promoted by Pleistocene climate fluctuations and geographic isolation. The acute rising of the Hengduan Mountain with the entire uplift of the Qinghai-Tibet Plateau induced the initial differentiation of Pseudovelia species. These results highlighted the importance of geographical isolation and climate changes in promoting speciation in mountain habitat islands.