By solving the Schrödinger equation and the Poisson equation self-consistently, we have calculated the electronic structure for the Si-uniformally-doped GaAs/AlGaAs quantum well system at T=273 K and B=25 T in the effective mass approximation. We also studied the influence of the temperature and the external magnetic field on the subband energies, eigen-envelope functions, self-consistent potential, density distribution of the electrons, and the Fermi energy. It is found that at the given magnetic field B≠0, with the increase of temperature, the subband energies increase monotonically, the Fermi energy decreases monotonically, the width of the self-consistent potential well decreases, the depth of the well increases, the distribution of the electron density becomes wider, and the peak value is reduced. At the given temperature, with the increase of the strength of the magnetic field, the subband energies and Fermi energy increase monotonically, the depth of the self-consistent potential well is reduced, the peak of the electron density distribution becomes higher, and concentrated around the center of the well.