The arrangement of cation atoms in the observed high-resolution images of a superconductor Bi-Ca-Sr-Cu-O is interpreted well with the Bi//4Ti//3O//1//2-type structure which consists of doubled slabs of the perovskite structure unit separated by double layers of Bi atoms. Some defects considered as intergrowths of polymorphic structures with different numbers of perovskite layers were observed. From the observed images and electron diffraction patterns, we proposed a structural model with an ordered arrangement of oxygen atoms.