The one-dimensional self-consistent simulation of the band diagram and carrier distribution of the AlGaN/GaN double hetero-structure is firstly carried out to research the effect of the thickness and Al content of the AlGaN back-barrier layer on the carrier distribution. Then the AlGaN/GaN double hetero-structure materials with different back-barrier layers were grown by low-pressure MOCVD method on c-plane sapphire substrate. The mercury probe CV measurement was carried out to verify the results of theoretical simulation. The results of theoretical simulation and experiment both indicate that with the increase of Al content and thickness of the AlGaN back-barrier layer, the two-dimensional electron Gas density becomes low in the main channel and high in the parasitic channel gradually.The increase of Al content and thickness of the AlGaN back-barrier layer effectively enhances the two-dimensional electron Gas confinement but simultaneity produces higher-density parasitic channel. So a compromise has to be made between the improvement of the two-dimensional electron Gas confinement and the restraint of the carrier density in parasitic channel in designing the double heterostructure.