One-dimensional swelling deformation tests, collapse tests and swell pressure tests due to wetting were carried out on Gaomiaozi sodium bentonite by using oedometer, for analyzing the swelling and collapse deformation characteristics of mixtures of bentonite and quartz sand in different sand additions. Based on the concept of the montmorillonite void ratio, the deformation characteristics of bentonite-sand mixtures at saturation were consistently identified. Test results indicated that when the content of sand in the mixture was small, the relationship between the montmorillonite void ratio and vertical pressure at saturation was a straight line in the log scales. According to this line, the swelling deformation and pressure can be predicted when the bentonite or its mixtures at different dry densities or mixing ratios absorb water till saturation. Test results of the mixture with high sand fractions were analyzed by using the sand skeleton void ratio, which could predict whether the sand skeleton forms and the vertical pressure when the sand skeleton begins to form.