By using a diamond-anvil cell (DAC) with laser heating technology, a cubic perovskite polymorph of SrSiO3 has been synthesized at similar to 38 GPa and 1500-2000 K for the first time. The P-V data of this new phase give ambient temperate elastic constants of V-0 = 49.18(5) angstrom(3), K-0 = 211(3) GPa, respectively, when they are fitted against the Birch-Murnaghan equation of state with a fixed K-0' at 4. On decompression, the SrSiO3 cubic perovskite phase becomes unstable at similar to 6.2 GPa and disappears completely at similar to 4.7 GPa. The transformed product can be considered as an amorphous phase with a minor amount of small sized crystals in the amorphous matrix. First principle calculations predicted structural properties of both the cubic and the six-layer-repeated hexagonal perovskite polymorphs of SrSiO3 in good agreement with experimental results. The experimental and theoretical results indicate that the larger Sr2+ cation can substitute the Ca2+ cation and enter into the lattice of the cubic perovskite phase of CaSiO3 at lower mantle conditions with only a small lattice strain. These results indicate that Sr can be hosted in cubic perovskite CaSiO3 found as inclusions in diamonds originating from the lower mantle.