In this paper, nanowire core-shell AlGaN/GaN heterostructures were designed and the effects of potential barrier layer thickness, Al component, and doping concentration on the concentration of two-dimensional electron gas (2DEG) in the planar as well as nanowire heterostructures were studied. The results show that, the rise rate of 2DEG concentration in both structures slow down as the thickness of potential barrier layer increases, and when the thickness reaches 40 nm, the 2DEG concentration gradually stabilizes due to the complete emission of surface state electrons. With the increase of Al component, the polarization effect is gradually enhanced, which makes the 2DEG concentration at the heterogeneous interface of both structures gradually increase. When the doping concentration gradually increases, it can be found that potential difference at the heterogeneous interface increases, the potential well deepening and the ability strengthening for bound electron, which finally lead to the gradual increase of 2DEG concentration. The 2DEG surface density reaches its maximum value as the doping concentration increases to 2.0×1018 cm-3. Compared with the planar structure, the nanowire structure can achieve a higher Al component, and the 2DEG surface density can reach up to 5.13×1013 cm-2 under the high Al component, which is a large improvement.