Species-level paraphyly inferred from mitochondrial gene trees is a prevalent phenomenon in phylogenetics and phylogeography, but there are several potential causes (e.g. deep coalescence, introgression) representing various evolutionary processes. Previous molecular systematics on P. ruficollis also suggested plausible mitochondrial-gene-tree paraphyly of Pomatorhinus ruficollis (on Asian mainland and Hainan I.) with respect to P. musicus, but with low supports. To further verify this phylogenetic pattern and to clarify its potential causes, subsequent analyses were conducted with extensive gene sampling as four mtDNA (totally 3054bp) and nuDNA (totally 4930bp) and using three kinds of coalescent-based simulations. Phylogenetic reconstruction based mtDNA retrieved affinity of P. musicus and EAST clade of P. ruficollis with robust support. All simulation analyses suggest the cause of observed mitochondrial gene-tree paraphyly resulted from unidirectional gene flow from mainland to Taiwan. Mitochondrial capture theory proposed would provide a framework for future studies. This work was supported by the National Natural Science Foundation of China.