The two-dimensional electron-gas (2DEG) distribution, sheet density and subband occupations in AlxGa1-xN/GaN heterostructure are calculated by solving the coupled Schrdinger and Poisson equations selfconsistently. By involving degree of relaxation to distinguish the spontaneous and piezoelectric polarizations, the influence of the polarizations and the doping in the AlGaN barrier on the 2DEG properties are investigated separately. It is found that the 2DEG properties depend much stronger on the polarizations than on the doping, and that the contribution of the spontaneous polarization is dominant. The 2DEG sheet density is calculated to be 1.6×10-13cm-2 with an Al-content of x=0.3 in the strained AlGaN barrier, the contributions of spontaneous and piezoelectric polarizations are 0.9×10-13 and 0.7×10-13cm-2 respectively. When the doping of the AlGaN barrier is increased from 1×10-17 to 1×10-18cm-3, the 2DEG sheet density is increased by 0.2×10-13cm-2