Taking the form of Gibbs energy functions in the SGTE (Scientific Group Thermodata Europe) database of pure elements, adopting the newly available thermochemical reference data of JANAF (Joint Army-Navy-Air Force) database, the correction of transition data and reassessment of the parameters of Gibbs energy of elemental Si have been performed with the least-square method. The results agree more accurately with JANAF data than with the SGTE data. At the same time, the lattice stability parameters obtained by the CALPHAD method in the SGTE database have been extrapolated to 0 K, and these results have been compared with those of the total energy plane wave pseudopotential method and projector augmented wave method in first principles．It was found that the result of the total energy plane wave pseudopotential method agrees with that of CALPHAD, ＞ ＞ ＞0. Besides, it was found that the results of lattice constants and atomic volumes of diamond-Si calculated by the total energy plane wave pseudopotential method were much larger than experimental data and those of fcc-, hcp- and bcc-Si were smaller than those by the projector augmented wave method in first principles. The same case occurred in total energy calculations. All the electrons in valence distribute in the energy zone from －15 to 0 eV, part of s state electrons per atom in diamond-, fcc-, hcp-, and bcc-Si are changed into p state electrons, and diamond-Si has the largest number of transition and is the most stable phase, which were further proved by the results of density of state calculations.

Key words: Si, Gibbs energy, least-square method, lattice stability, first principles