Late Paleozoic A-type granites are widely distributed in Hegenshan-Heihe segment of the Inner Mongolia-Greater Hinggan Mountains orogenic belt. Their tectonic environments and petrogenesis remain controversial. A-type granites in Hegenshan-Heihe segment were emplaced in Late carboniferous-Permian period(325~260Ma), and the magmatic activities entered into the peak period in Permian. The A-type granite belt is metaluminous or slightly peraluminous (A/CNK=0.89~1.13) and belongs to the high-K, calc-alkaline series. Researches show that the ancient Asian oceanic plate still subducted into the Siberia plate between Late carboniferous and Permian, so the subducton-related back-arc extensional environment is thought to have been responsible for the formation of Hegenshan-Heihe A-type granites. The continental back-arc extension was probably related to the subduction slab rollback or the break-off induced upwelling of hot asthenospheric mantle.