Abstract: Phase equilibria data of the ternary Na₂SO₄-Na₂S₂O₃-H₂O,Na₂S₂O₃-NaSCN-H₂O and Na₂SO₄-NaSCN-H₂O systems at 313.15 K were determined by the isothermal dissolution equilibrium method.The equilibrium solid phases were determined by X-ray spectroscopy,and the phase diagrams of the ternary systems were drawn.There is no double salt or solid solution formed,and the three systems belong to a simple eutectic system.The phase diagrams of the ternary systems have one invariant point and two univariant curves at the boundary of two crystallization fields.The equilibrium solid phase of Na₂SO₄-Na₂S₂O₃-H₂O is composited of sodium sulfate(Na₂SO₄) and sodium thiosulfate pentahydrate (Na₂S₂O₃·5H₂O),respectively.Sodium thiosulfate pentahydrate and sodium rhodanate (NaSCN) are the components of the solid phase of Na₂S₂O₃-NaSCN-H₂O,and the solid phase of Na₂SO₄-NaSCN-H₂O consists of sodium sulfate and sodium rhodanate.The experimental results suggest that Na₂S₂O₃ and NaSCN show an obvious decrease of the solubility of Na₂SO₄.