Abstract: In order to clearly comprehend the volume change law of sulphate saline soil in the intense reaction period of producing ice crystals and causing salt expansion, assuming that the ice crystals and the mirabilite in the soil exist independently and the volume change of soil is composed of three increased parts and three reduced parts, and based on the law of conservation of solute, an expression for the volume change of sulphate saline soil considering salt expansion and frost heave is proposed. It is found that the expression for the volume change in the intense reaction period is largely decided by the initial void ratio n, unfrozen water content θ_u1 and θ_u2 before and after being cooled, and solubility r₁ and r₂ before and after being cooled. The volume of artificial sulphate saline soil samples is investigated using the test system of soil under controlled temperature. The unfrozen water content in the process of freezing is determined by the freezing temperature tests, and the concept of no precipitated water content (NPWC) is given, and the cumulative volume change rate of soil samples during being cooled is calculated. The rationality and applicability of the proposed expression is verified through analysis and comparison between the measured and calculated volume change rates of soil samples.