By using diaryliodonium salts, a novel approach of a palladium-catalyzed cascade of diarylation/intramolecular dehydrogenative coupling reaction has been developed in the synthesis of phenanthro-imidazopyridine fused heteropolycycles. The method can tolerate various substrates, and the target products were rapidly constructed in one pot. Furthermore, studies of the detailed reaction mechanism provide an insight into the C-H functionalization of 2-aryl-imidazopyridine derivatives and the C-C bond formations in the presence of palladium catalyst.