Abstract: This paper examines the expansive soil shear strength improved with weathered sand by indoor direct shear test. It studies the modified expansive soil shear strength parameters and the the relationship of the normal stress and the shear stress under different vertical loads, different sand proportions and different moisture contents. The two key factors that affect the direct shear test results is the vertical load and shear rate test. Existing norms of the shear rate is clearly defined, but the vertical load only a recommended value. The expansive soils were mixed with 10%, 20%, 30%, 40%, 50% of the weathered sand, respectively and matched with 6%, 8%, 10%, 12%, 14%water contents. They were loaded under the level I(12.5～50kPa),level Ⅱ(62.5～100kPa),or level Ⅲ(100～400kPa) of vertical loads for the shear test. The test results give the following findings. Vertical load has a high impact on the improved expansive soil shear strength parameters. When the vertical load is reduced, the angle of the soil internal friction gradually increases but its cohesion gradually decreases. At all the levels under the vertical load and the moisture content in the same condition, the cohesive force gradually decreases with the increase of the mixed sand ratio, and the angle of internal friction initially increases and then decreases. In the same sand proportion, the cohesive force and angle of internal friction first increase and then decrease as the moisture content increases. The research results provide a test basis for using weathered sand to improve expansive soil for highway roadbed filler.