Based on eight-point cluster variation method and introduction of isotropic nearest neighbor interaction and anisotropic next nearest neighbor interactions, the orderdisorder phase transition phenomena of the □-O (□: oxygen vacancy; O: oxygen) system on the copper-oxygen plane between two Ba-layers were studied. Calculation results show that there is not only a superconducting orthohombic phase (I) near z = 7.0, but also a superconducting orthohombic phase (II) near z = 6.5, as well as other metastable phases.