By self-consistently sovling the coupled Schrdinger and Poisson equations, we have investingated the property of the two-dimensional electron gases (2DEG) in AlxGa1-xN/GaN heterostructures. We demonstrate the depen dence of the density, the distribution, and the subband occupation of the 2DEG on the Al-content of the AlGaN barrier. Band offset and mechanism of spontaneous and piezoelectric polarization were concerned to discuss our results.