Abstract: ByX-ray powder diffraction technique and oxygen content analysis, a solid solution Sm_1+xBa_2-xCu₃O_y was determined with the solid solution region in 0 ≤ x ≤ 0.4. When x<0.25, the Sm_1+xBa_2-xCu₃O_y presents orthorhombic symmetry, and the orthorhombic-tetragonal transition occurs at x=0. 25. With the increase of x, T_c decreases and finally breaks off. The correlation between oxygen content and phase structure at different quench temperature related to SmBa₂Cu₃O_y, was investigated as well.