The electron density maps of twin-free orthorhombic YBa2Cu3O7-x single crystal were calculated from the refinement of X-ray structure analysis. The YBa2Cu3O7-x single crystal was grown by the top-seeded crystal pulling method. Uniaxial pressure was applied in oxygen annealing process to manufacture a twin-free orthorhombic single crystal. The crystal structures of YBa2Cu3O7-x with a superconducting transition temperature of 91 K were determined by four-circle X-ray diffractometer. Crystal data: Mr: 666.4, orthorhombic, Pmmm, a = 3.8278 (7), b = 3.8952 (7), c = 11.711 (2) A, V = 174.61 (5) A^3, Z = 1, Dx = 6.317 Mgm^-3 λ(MoKa) = 0.71069 A, μ(MoKa) = 282.77 cm-' . The final values of the weighted reliability factor (Rw) and unweighted factor (R) were 0.031 and 0.026 enable us to analyze Fourier difference maps.