Subsolidus phase relation and crystal structure in the Pr_1-xBa_2-yCa_x+yCu₃O_7±δ system were studied by X-ray diffraction combined with Rietveld structure refinement. The results indicate that all of the Pr_1-xBa_2-yCa_x+yCu₃O_7±δ (y=0) samples contain a BaCuO₂ phase besides the Pr123 (PrBa₂Cu₃O_7±δ) phase under 950 ℃ in the air. Furthermore, the content of the BaCuO₂ phase increases with increasing Ca content. The samples of Pr_1-xBa_2-yCa_x+yCu₃O_7±δ (x=0) (y=0.1, 0.2, 0.3, 0.4) contain only one phase, Pr123, except for the sample with y=0.5 which contains three phases, Pr123, Ca₂CuO₃ and Pr₄Ca₁₀Cu₂₄O₄₁. Otherwise, the Pr123 structure takes place the orthorhombic-tetragonal transition in the Pr_1-xBa_2-yCa_x+yCu₃O_7±δ (x=0) system (y=0.1, 0.2, 0.3, 0.4) with increasing Ca ion content. The structure of the Pr_1-xBa_2-yCa_x+yCu₃O_7±δ (x=0) samples with y=0.1 and 0.2 is orthorhombic. The lattice parameters are a=0.390 33(4)~0.389 36(1) nm, b=0.389 53(4)~0.387 73(1) nm, c=1.173 38(4)~1.168 20(2) nm; The structure of the Pr_1-xBa_2-yCa_x+yCu₃O_7±δ (x=0) samples with x=0.3 and 0.4 is tetragonal. The lattice parameters are a=b=0.387 80 (0), 0.387 67 (0) nm, c=1.166 00 (2), 1.165 20 (2) nm. In the Pr123 structure, Ba ions could be replaced by Pr ions, but could not be replaced by Ca ions. Ca ions partially occupy the sites of Pr ions. The ionic radius plays a more important role than the chemical properties in the mutual substitution of Pr, Ba and Ca ions in the Pr123 structure of the Pr_1-xBa_2-yCa_x+yCu₃O_7±δ. The highest content of Ca ions in the Pr_1-xBa_2-yCa_x+yCu₃O_7±δ system is x=0, y=0.4 under 950 ℃ in air.