Abstract: The change of hydrochemical environment of granite residual soil will affect its physical and mechanical properties and microstructure. In order to explore the effects of immersion in Na₂SO₄ solution with different concentrations for 7 and 14 days on the physical and mechanical properties of the granite residual soil, the self-developed water and soil chemical cycle system is used to study the change rules of its resistivity, boundary moisture content, compressibility, shear strength, mineral composition and microstructure. The tests show that increasing the concentration of Na₂SO₄ solution can reduce its resistivity and limit moisture content. With the increase of the salt concentration, the compressibility of the granite residual soil increases first and then decreases after soaked for 7 days. When soaked for 14 days, the compressibility of the granite residual soil exhibits an overall upward trend. The shear strength, cohesion and internal friction angle first decrease and then increase with the increase of the salt concentration. After soaked for 14 days, the internal friction angle of the granite residual soil increases as the salt concentration increases. The SEM images show that the granite residual soil is in flocculation structure after soaked in Na₂SO₄ solution, and the soil particles are obviously coarsened. The research results may provide a certain reference value for the change laws of physical and mechanical properties of Na₂SO₄ solution after it affects the soil.