Abstract: Barium titanate is an important ferroelectric and its dielectric constant is the highest near the Curie point of 130 ℃. In order to reduce the Curie point of barium titanate, strontium is usually doped in barium titanate. Barium titanate powder was prepared with hydrothermal synthesis, and a 2×2×1 supercell was established for first-principles calculations. The rightward shift of the XRD diffraction peak with the increase of doped strontium indicates that the unit cell structure of barium strontium titanate gradually changes from tetragonal phase to cubic phase. The calculated results show that the unit cell parameters of barium titanate are gradually reduced. The ratio of the unit cell parameters c to a gradually decreases, which is consistent with the experiment; the gradual weakening of the Raman spectral peak indicates that the degree of spontaneous polarization of barium titanate is gradually weakened. It is found that the displacements of Ti and O from the body-center and face-center respectively are gradually reduced. Because the atomic radius of strontium is smaller than that of barium, after the barium is replaced by strontium in the unit cell, the unit cell parameters will become smaller, which hinders the spontaneous displacement of Ti. Ti only needs lower thermal vibration energy to overcome the Coulombic interaction with O and located in the center of the unit cell steadily. So the Curie temperature(Curie points) of barium strontium titanate will fall with the increase of doped strontium.