Abstract: A general model is proposed to simulate the dependence of void ratio on matric suction for unsaturated soils. This model can be derived based on (i) the characteristics and the relationship between soil-water characteristic curve (SWCC) and soil shrinkage characteristic curve (SSCC) and (ii) a SSCC formula using a three-segment linear model, and a three-phase basic formula for unsaturated soils. A series of unsaturated tests are conducted by using the triaxial apparatus on a red clay to further verify the theoretical assumption required for the proposed model. Only one parameter u is required in the theoretical assumption and has a clear physical meaning, which can be calibrated using the conventional SWCC tests. Based on the assumption with the amount of drainage of saturated samples at a given suction, the bulk volume change, the amount of the air entry into the soil and the total volumetric strain can be accurately predicted. The validity and application of the assumption are demonstrated by these tests, and hence the proposed assumption-based model is also validated.