Based on the generalized gradient approximation (GGA), the totalenergy, overlap populations and valence charges in the case of Ti atoms moving along c axi s in cubic and tetragonal phases were calculated by using ultrasoft pseudopotent ials (USP) plane wave method. It was demonstrated that the energy of tetragonal BaTiO3 was the lowest when Ti atoms move along the c axis by up to 0012n m, and the spontaneous polarization was 0261C/m2 , which was consistent with experimental results. Moreover, it was also confirmed that the ferroelectric st ability of BaTiO3 could be attributed to the orbital hybridization of 2p orbit of oxygen atom and 3d orbit of Ti atom.