Pressure induced phase transitions were found in spin ladder compounds SrCu₂O₃ and Sr₂Cu₃O₅ by powder X-ray diffraction (XRD) experiment with diamond anvil cell (DAC) and synchrotron radiation. The structure of the HP phase of SrCu₂O₃ was successfully solved by Rietvelt analysis. In the orthorhombic structure (space group Pmmn) with unit-cell parameters of a=10.628Å, b=3.885Å and c=3.282Å, the Cu₂O₃ planes at SrCu₂O₃ became "fluttering" as that of CaCu₂O₃. Application of an external pressure induced a structural transition as a substitution of smaller cation (Ca for Sr) did.