Topsoil slide and instability of expansive soil slopes may occur under variable saturation conditions.In order to study the strength characteristics of unsaturated expansive soil under low stress conditions，several different matrix suction and stress conditions were set by unsaturated triaxial apparatus.The triaxial shear test of Hefei expansive soil was carried out，and the test data were analyzed.The test results show that when the net confining stress on the expansive soil continues to weaken，the stress-strain curve transitions from strain hardening to strain softening.The strength of unsaturated expansive soil increases with increasing matrix suction.The shear strength of shallow expansive soil shows a significant reduction with non-linear characteristics.The cohesion of unsaturated expansive soils has a significant effect on the shear strength.The cohesion decreases significantly under low stress conditions，and the internal friction angle increases significantly.The net confining stress significantly affects the strength of the soil at the low stress level，but matrix suction has a weak effect on the strength of the soil at the low stress level.