The Ba2CuO3.3 sample with the nominal composition was synthesized. Powder X-ray diffraction (XRD) experiments confirm that it crystallizes in an orthorhombic structure with space group Immm. The synchrotron powder XRD results suggest that the crystal structure of Ba2CuO3.3 keeps stable under pressure up to 34 GPa at room temperature with nearly isotropic compressibility. The equation of state for Ba2CuO3.3 was obtained. The results offer opportunities to further synthesize and research Ba2CuO3+delta superconductor with tetragonal K2NiF4 structure.